I've always been partial to <a href="http://ipchicken.com" rel="nofollow">http://ipchicken.com</a> . It's got commercial motives, but it's easy to spell, it's easy to ask people to go to it and have them remember, and the numbers are giant and readable. This is all good!
For some additional crap, check <a href="http://www.ipspotting.com/" rel="nofollow">http://www.ipspotting.com/</a> - also easy to remember and fun in new places.