curl ifconfig.co
curl icanhazip.com
curl ifconfig.me
curl http://smart-ip.net/myip
telnet myip.gelma.net
dig +short @resolver1.opendns.com myip.opendns.com
dig +short @ns1.google.com -t txt o-o.myaddr.l.google.com
Note that myip.gelma.net does not resolve any more, so the telnet trick now fails.