A lot of times, when I’m trying to get the IP address of a computer, I use a small site called jsonip.com, which presents a nice (ad-free) JSON formatted IP address for viewing.

You can use it programmatically obviously, and it even supports JSONP (see: http://jsonip.com/func) - but I find I use it more often for a clear, easy-to-read IP address site (which far surpasses the ad-loaded junk you’ll find elsewhere).