Similar listings, etc. found on The Internet:
https://bushart.org/resource/public-ip-using-dns/
https://52.0.56.137.sslip.io/#experimental
https://sysop.user.uucp.hu/programs/doc/extip.txt program: https://github.com/bandie91/extip

Publicly available resources to check:

DNS column: U or T indicates respectively UDP or TCP only

May/probably going away ~2025-04-01 (not yet (all) gone as of 2025-04-17):
ip4.me, ip4only.me
ip6addr.com, ip6addr.net, ip6addr.org
ip6.me, ip6only.me
ipv6addr.com, ipv6addr.net, ipv6addr.org
onlyip4.me, onlyip6.me
whatismyipv6address.com, whatismyipv6address.net, whatismyipv6address.org
whatismyv6.com, whatismyv6.net, whatismyv6.org
per
https://www.reddit.com/r/ipv6/comments/1j5lrou/ip6me_and_related_sites_will_become_unavailable/
https://news.ycombinator.com/item?id=43256298
etc.

I'm hoping/intending to replace this wiki page with a list that's automagically maintained,
and also includes ability to programmatically accept submissions/updates.
Thus far it's still a work-in-progress.

myv4="$(curl -4 -s https://ipv4.balug.org/myip)"
myv6="$(curl -6 -s https://ipv6.balug.org/myip)"
control_M="$(printf '\015')"
for path in \
  1.1.1.1/cdn-cgi/trace \
  ifconfig.co/ \
  whatismyip.akamai.com/ \
  dafuqismyip.com/ \
  {,ipv4.,ipv6.}icanhazip.com/ \
  ipchicken.com/ \
  www.moanmyip.com/ \
  myexternalip.com/raw \
  simplesniff.com/ip \
  wgetip.com/ \
  whatsmyfuckingip.com/ \
  wtfismyip.com/text \
  ifconfig.io/ \
  ipinfo.io/ip \
  ident.me \
  ifconfig.me/ \
  ip.me/ \
  ip{4,6}{,only}.me/api/ \
  ipecho.net/plain \
  tnx.nl/ip \
  ip.tyk.nu/ \
  corz.org/ip \
  {,ipv{4,6}.}balug.org/myip \
  api.ipify.org/ \
  ip.42.pl/raw \
  {,ipv{4,6}.}pry.sh/ \
  {self{,6}.ip,myipv{4,6}}.addr.tools/ \
  myip.wtf/text
do
  for scheme in http https
  do
    for v in 4 6
    do
      case "$v" in
        4)
          myip="$myv4"
        ;;
        6)
          myip="$myv6"
        ;;
      esac
      curlopts="-"$v" -m 15 -s"
      r=$(curl $curlopts "$scheme://$path")
      case "$r" in
        "$myip")
          echo "\$ curl $curlopts $scheme://$path"
          echo $r
        ;;
        "$myip$control_M")
          echo "\$ curl $curlopts $scheme://$path"
          echo $myip'^M'
        ;;
        *"$myip"*)
          echo "\$ curl $curlopts $scheme://$path"
          echo $myip found in text
        ;;
        *)
          myRE=$(
            echo "$myip" |
            sed -e 's/[.:]/-/g'
          )
          printf '%s' "$r" |
          if grep "$myRE" >>/dev/null; then
            echo "\$ curl $curlopts $scheme://$path"
            echo $myip found in text in alternative format
          elif [ "$scheme" = https ]; then
            curlopts="-$v -k -m 15 -s"
            r=$(curl $curlopts "$scheme://$path")
            case "$r" in
              "$myip")
                echo "\$ curl $curlopts $scheme://$path # (https cert issue)"
                echo $r
              ;;
              "$myip$control_M")
                echo "\$ curl $curlopts $scheme://$path # (https cert issue)"
                echo $myip'^M'
              ;;
              *"$myip"*)
                echo "\$ curl $curlopts $scheme://$path # (https cert issue)"
                echo $myip found in text
              ;;
              *)
                myRE=$(
                  echo "$myip" |
                  sed -e 's/[.:]/-/g'
                )
                printf '%s' "$r" |
                grep "$myRE" >>/dev/null && {
                  echo "\$ curl $curlopts $scheme://$path"
                  echo $myip found in text in alternative format
                }
              ;;
            esac
          fi
        ;;
      esac
    done
  done
done; echo '$ '

$ curl -4 -m 15 -s https://1.1.1.1/cdn-cgi/trace
96.86.170.226 found in text
$ curl -4 -m 15 -s http://ifconfig.co/
96.86.170.226
$ curl -6 -m 15 -s http://ifconfig.co/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ifconfig.co/
96.86.170.226
$ curl -6 -m 15 -s https://ifconfig.co/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://whatismyip.akamai.com/
96.86.170.226
$ curl -4 -k -m 15 -s https://whatismyip.akamai.com/ # (https cert issue)
96.86.170.226
$ curl -4 -m 15 -s https://dafuqismyip.com/
96.86.170.226^M
$ curl -6 -m 15 -s https://dafuqismyip.com/
2001:470:67:76f::2^M
$ curl -4 -m 15 -s http://icanhazip.com/
96.86.170.226
$ curl -6 -m 15 -s http://icanhazip.com/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://icanhazip.com/
96.86.170.226
$ curl -6 -m 15 -s https://icanhazip.com/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ipv4.icanhazip.com/
96.86.170.226
$ curl -4 -m 15 -s https://ipv4.icanhazip.com/
96.86.170.226
$ curl -6 -m 15 -s http://ipv6.icanhazip.com/
2001:470:67:76f::2
$ curl -6 -m 15 -s https://ipv6.icanhazip.com/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ipchicken.com/
96.86.170.226 found in text
$ curl -4 -m 15 -s https://www.moanmyip.com/
96.86.170.226 found in text
$ curl -6 -m 15 -s https://www.moanmyip.com/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s http://myexternalip.com/raw
96.86.170.226
$ curl -6 -m 15 -s http://myexternalip.com/raw
2001:470:67:76f::2
$ curl -4 -m 15 -s https://myexternalip.com/raw
96.86.170.226
$ curl -6 -m 15 -s https://myexternalip.com/raw
2001:470:67:76f::2
$ curl -4 -k -m 15 -s https://simplesniff.com/ip # (https cert issue)
96.86.170.226
$ curl -4 -m 15 -s http://wgetip.com/
96.86.170.226
$ curl -6 -m 15 -s http://wgetip.com/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://wgetip.com/
96.86.170.226
$ curl -6 -m 15 -s https://wgetip.com/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://whatsmyfuckingip.com/
96.86.170.226 found in text
$ curl -4 -m 15 -s http://wtfismyip.com/text
96.86.170.226
$ curl -6 -m 15 -s http://wtfismyip.com/text
2001:470:67:76f::2
$ curl -4 -m 15 -s https://wtfismyip.com/text
96.86.170.226
$ curl -6 -m 15 -s https://wtfismyip.com/text
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ifconfig.io/
96.86.170.226
$ curl -6 -m 15 -s http://ifconfig.io/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ifconfig.io/
96.86.170.226
$ curl -6 -m 15 -s https://ifconfig.io/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ipinfo.io/ip
96.86.170.226
$ curl -4 -m 15 -s https://ipinfo.io/ip
96.86.170.226
$ curl -4 -m 15 -s http://ident.me
96.86.170.226
$ curl -6 -m 15 -s http://ident.me
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ident.me
96.86.170.226
$ curl -6 -m 15 -s https://ident.me
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ifconfig.me/
96.86.170.226
$ curl -6 -m 15 -s http://ifconfig.me/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ifconfig.me/
96.86.170.226
$ curl -6 -m 15 -s https://ifconfig.me/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ip.me/
96.86.170.226
$ curl -6 -m 15 -s http://ip.me/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ip.me/
96.86.170.226
$ curl -6 -m 15 -s https://ip.me/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://ip4.me/api/
96.86.170.226 found in text
$ curl -4 -m 15 -s https://ip4.me/api/
96.86.170.226 found in text
$ curl -4 -m 15 -s http://ip4only.me/api/
96.86.170.226 found in text
$ curl -4 -m 15 -s https://ip4only.me/api/
96.86.170.226 found in text
$ curl -4 -m 15 -s http://ip6.me/api/
96.86.170.226 found in text
$ curl -6 -m 15 -s http://ip6.me/api/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s https://ip6.me/api/
96.86.170.226 found in text
$ curl -6 -m 15 -s https://ip6.me/api/
2001:470:67:76f::2 found in text
$ curl -6 -m 15 -s http://ip6only.me/api/
2001:470:67:76f::2 found in text
$ curl -6 -m 15 -s https://ip6only.me/api/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s http://ipecho.net/plain
96.86.170.226
$ curl -6 -m 15 -s http://ipecho.net/plain
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ipecho.net/plain
96.86.170.226
$ curl -6 -m 15 -s https://ipecho.net/plain
2001:470:67:76f::2
$ curl -4 -m 15 -s http://tnx.nl/ip
96.86.170.226 found in text
$ curl -6 -m 15 -s http://tnx.nl/ip
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s https://tnx.nl/ip
96.86.170.226 found in text
$ curl -6 -m 15 -s https://tnx.nl/ip
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s http://ip.tyk.nu/
96.86.170.226
$ curl -6 -m 15 -s http://ip.tyk.nu/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://ip.tyk.nu/
96.86.170.226
$ curl -6 -m 15 -s https://ip.tyk.nu/
2001:470:67:76f::2
$ curl -4 -m 15 -s https://corz.org/ip
96.86.170.226
$ curl -4 -m 15 -s http://ipv4.balug.org/myip
96.86.170.226
$ curl -4 -m 15 -s https://ipv4.balug.org/myip
96.86.170.226
$ curl -6 -m 15 -s http://ipv6.balug.org/myip
2001:470:67:76f::2
$ curl -6 -m 15 -s https://ipv6.balug.org/myip
2001:470:67:76f::2
$ curl -4 -m 15 -s http://api.ipify.org/
96.86.170.226
$ curl -4 -m 15 -s https://api.ipify.org/
96.86.170.226
$ curl -4 -m 15 -s http://ip.42.pl/raw
96.86.170.226
$ curl -4 -m 15 -s https://ip.42.pl/raw
96.86.170.226
$ curl -4 -m 15 -s http://pry.sh/
96.86.170.226 found in text
$ curl -6 -m 15 -s http://pry.sh/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s https://pry.sh/
96.86.170.226 found in text
$ curl -6 -m 15 -s https://pry.sh/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s http://ipv4.pry.sh/
96.86.170.226 found in text
$ curl -4 -m 15 -s https://ipv4.pry.sh/
96.86.170.226 found in text
$ curl -6 -m 15 -s http://ipv6.pry.sh/
2001:470:67:76f::2 found in text
$ curl -6 -m 15 -s https://ipv6.pry.sh/
2001:470:67:76f::2 found in text
$ curl -4 -m 15 -s http://self.ip.addr.tools/
96.86.170.226 found in text in alternative format
$ curl -4 -m 15 -s https://self.ip.addr.tools/
96.86.170.226 found in text in alternative format
$ curl -6 -m 15 -s http://self6.ip.addr.tools/
2001:470:67:76f::2 found in text in alternative format
$ curl -6 -m 15 -s https://self6.ip.addr.tools/
2001:470:67:76f::2 found in text in alternative format
$ curl -4 -m 15 -s http://myipv4.addr.tools/
96.86.170.226
$ curl -4 -m 15 -s https://myipv4.addr.tools/
96.86.170.226
$ curl -6 -m 15 -s http://myipv6.addr.tools/
2001:470:67:76f::2
$ curl -6 -m 15 -s https://myipv6.addr.tools/
2001:470:67:76f::2
$ curl -4 -m 15 -s http://myip.wtf/text
96.86.170.226
$ curl -6 -m 15 -s http://myip.wtf/text
2001:470:67:76f::2
$ curl -4 -m 15 -s https://myip.wtf/text
96.86.170.226
$ curl -6 -m 15 -s https://myip.wtf/text
2001:470:67:76f::2
$ 

myv4="$(curl -4 -s https://ipv4.balug.org/myip)" || exit
myv6="$(curl -6 -s https://ipv6.balug.org/myip)" || exit
control_M="$(printf '\015')"
#digopts='+noall +answer +nottl +norecurse'
digopts='+short +norecurse'
for ns_rr_class_types in \
  '1.1.1.1 whoami.cloudflare CH TXT' \
  'ns1.google.com. o-o.myaddr.l.google.com. IN TXT' \
  'resolver1.opendns.com. myip.opendns.com. IN A AAAA' \
  'ns.sslip.io. ip.sslip.io. IN TXT' \
  'update.dynamic.name. my.dynamic.name. IN A' \
  'ns1-1.akamaitech.net. whoami.akamai.net. IN A' \
  'one.one.one.one. whoami.cloudflare. CH TXT' \
  'dns.toys ip. IN TXT'
do
  set -- $ns_rr_class_types
  NS="$1"; shift; RR="$1"; shift; CLASS="$1"; shift; TYPES="$*"
  for TYPE in $TYPES
  do
    query="$RR $TYPE $CLASS"
    for v in 4 6
    do
      case "$v" in
        4)
          myip="$myv4"
        ;;
        6)
          myip="$myv6"
        ;;
      esac
      r=$(dig @"$NS" $digopts -"$v" $query 2>>/dev/null) &&
      case "$r" in
        \""$myip"\"|"$myip")
          echo "\$ dig @"$NS" $digopts -"$v" $query"
          echo $r
        ;;
        *"$myip"*)
          echo "\$ dig @"$NS" $digopts -"$v" $query"
          printf 'found in text:\n%s\n' "$r"
        ;;
        *)
          myRE=$(
            echo "$myip" |
            sed -e 's/[.:]/-/g'
          )
          printf '%s' "$r" |
          if grep "$myRE" >>/dev/null; then
            echo "\$ dig @"$NS" $digopts -"$v" $query"
            echo $myip found in text in alternative format
          fi
        ;;
      esac
      r=$(dig @"$NS" +tcp $digopts -"$v" $query 2>>/dev/null) &&
      case "$r" in
        \""$myip"\"|"$myip")
          echo "\$ dig @"$NS" +tcp $digopts -"$v" $query"
          echo $r
        ;;
        *"$myip"*)
          echo "\$ dig @"$NS" +tcp $digopts -"$v" $query"
          printf 'found in text:\n%s\n' "$r"
        ;;
        *)
          myRE=$(
            echo "$myip" |
            sed -e 's/[.:]/-/g'
          )
          printf '%s' "$r" |
          if grep "$myRE" >>/dev/null; then
            echo "\$ dig @"$NS" +tcp $digopts -"$v" $query"
            echo $myip found in text in alternative format
          fi
        ;;
      esac
    done
  done
done; echo '$ '
$ dig @1.1.1.1 +short +norecurse -4 whoami.cloudflare TXT CH
"96.86.170.226"
$ dig @1.1.1.1 +tcp +short +norecurse -4 whoami.cloudflare TXT CH
"96.86.170.226"
$ dig @ns1.google.com. +short +norecurse -4 o-o.myaddr.l.google.com. TXT IN
"96.86.170.226"
$ dig @ns1.google.com. +tcp +short +norecurse -4 o-o.myaddr.l.google.com. TXT IN
"96.86.170.226"
$ dig @ns1.google.com. +short +norecurse -6 o-o.myaddr.l.google.com. TXT IN
"2001:470:67:76f::2"
$ dig @ns1.google.com. +tcp +short +norecurse -6 o-o.myaddr.l.google.com. TXT IN
"2001:470:67:76f::2"
$ dig @resolver1.opendns.com. +short +norecurse -4 myip.opendns.com. A IN
96.86.170.226
$ dig @resolver1.opendns.com. +tcp +short +norecurse -4 myip.opendns.com. A IN
96.86.170.226
$ dig @resolver1.opendns.com. +short +norecurse -6 myip.opendns.com. AAAA IN
2001:470:67:76f::2
$ dig @resolver1.opendns.com. +tcp +short +norecurse -6 myip.opendns.com. AAAA IN
2001:470:67:76f::2
$ dig @ns.sslip.io. +short +norecurse -4 ip.sslip.io. TXT IN
"96.86.170.226"
$ dig @ns.sslip.io. +tcp +short +norecurse -4 ip.sslip.io. TXT IN
"96.86.170.226"
$ dig @ns.sslip.io. +short +norecurse -6 ip.sslip.io. TXT IN
"2001:470:67:76f::2"
$ dig @ns.sslip.io. +tcp +short +norecurse -6 ip.sslip.io. TXT IN
"2001:470:67:76f::2"
$ dig @update.dynamic.name. +short +norecurse -4 my.dynamic.name. A IN
96.86.170.226
$ dig @ns1-1.akamaitech.net. +short +norecurse -4 whoami.akamai.net. A IN
96.86.170.226
$ dig @ns1-1.akamaitech.net. +tcp +short +norecurse -4 whoami.akamai.net. A IN
96.86.170.226
$ dig @one.one.one.one. +short +norecurse -4 whoami.cloudflare. TXT CH
"96.86.170.226"
$ dig @one.one.one.one. +tcp +short +norecurse -4 whoami.cloudflare. TXT CH
"96.86.170.226"
$ dig @one.one.one.one. +short +norecurse -6 whoami.cloudflare. TXT CH
"2001:470:67:76f::2"
$ dig @one.one.one.one. +tcp +short +norecurse -6 whoami.cloudflare. TXT CH
"2001:470:67:76f::2"
$ dig @dns.toys +short +norecurse -4 ip. TXT IN
"96.86.170.226"
$ dig @dns.toys +short +norecurse -6 ip. TXT IN
"2001:470:67:76f::2"
$ 

myv4="$(curl -4 -s https://ipv4.balug.org/myip)" || exit
myv6="$(curl -6 -s https://ipv6.balug.org/myip)" || exit
control_M="$(printf '\015')"
for userathost in \
  sshmyip.com myip@{,ipv{4,6}.}balug.org
do
  for v in 4 6
  do
    case "$v" in
      4)
        myip="$myv4"
      ;;
      6)
        myip="$myv6"
      ;;
    esac
    sshopts="-$v -n -o BatchMode=yes -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null"
    r=$(ssh $sshopts $userathost 2>>/dev/null)
    case "$r" in
      "$myip")
        echo "\$ ssh -$v $userathost"
        echo $r
      ;;
      "$myip$control_M")
        echo "\$ ssh -$v $userathost"
        echo $myip'^M'
      ;;
      *"$myip"*)
        echo "\$ ssh -$v $userathost"
        echo $myip found in text
      ;;
      *)
        myRE=$(
          echo "$myip" |
          sed -e 's/[.:]/-/g'
        )
        printf '%s' "$r" |
        if grep "$myRE" >>/dev/null; then
          echo "\$ ssh -$v $userathost"
          echo $myip found in text in alternative format
        fi
      ;;
    esac
  done
done; echo '$ '
$ ssh -4 sshmyip.com
96.86.170.226 found in text
$ ssh -6 sshmyip.com
2001:470:67:76f::2 found in text
$ ssh -4 myip@balug.org
96.86.170.226
$ ssh -6 myip@balug.org
2001:470:67:76f::2
$ ssh -4 myip@ipv4.balug.org
96.86.170.226
$ ssh -6 myip@ipv6.balug.org
2001:470:67:76f::2
$ 

myv4="$(curl -4 -s https://ipv4.balug.org/myip)" || exit
myv6="$(curl -6 -s https://ipv6.balug.org/myip)" || exit
control_M="$(printf '\015')"
for domain in \
  telnetmyip.com
do
  for v in 4 6
  do
    case "$v" in
      4)
        myip="$myv4"
      ;;
      6)
        myip="$myv6"
      ;;
    esac
    telnetopts="-$v"
    r=$(sleep 2 | telnet $telnetopts $domain 2>>/dev/null)
    case "$r" in
      "$myip")
        echo "\$ telnet -$v $domain"
        echo $r
      ;;
      "$myip$control_M")
        echo "\$ telnet -$v domain"
        echo $myip'^M'
      ;;
      *"$myip"*)
        echo "\$ telnet -$v $domain"
        echo $myip found in text
      ;;
      *)
        myRE=$(
          echo "$myip" |
          sed -e 's/[.:]/-/g'
        )
        printf '%s' "$r" |
        if grep "$myRE" >>/dev/null; then
          echo "\$ telnet -$v $domain"
          echo $myip found in text in alternative format
        fi
      ;;
    esac
  done
done; echo '$ '
$ telnet -4 telnetmyip.com
96.86.170.226 found in text
$ telnet -6 telnetmyip.com
2001:470:67:76f::2 found in text
$