[hm2k]

http://whatismyip.akamai.com/

Pretty reliable.

[IsaacSchlueter]

Parsing text is too hard. It'd be easier if it was in JSON.

[gulbrandr]

Oh I see! This is what you are looking for: http://www.showmyip.com/xml/

[jdub]

Ha ha ha. :-)

[NovaDesu]

http://demontunes.com/api/?g=ip&format=json (&callback=name)