My computers are sitting behind a router/firewall. How do I programmatically find out what my external IP address is. I can use http://www.whatsmyip.org/ for ad-hoc queries, but the TOS don't allow for automated checks.
Any ideas?
Unfortunately as of 2013, whatismyip.com charge for the service.
http://www.icanhazip.com is still going strong, 3 years later. Just outputs the IP as text, absolutely nothing else.
http://checkip.dyndns.org still works as well.
You can also use Google if you want to be sure it won't go down, but it can still block you for TOS violations.
https://www.google.ie/search?q=whats+is+my+ip
But even when they block me, they still tell me my client IP address in the error message.