Hey,

I just came upon this place and it seems much better designed and handled than most. It even has a way for you to upload pictures of a bike. If the bike is found, anyone can search. It's free to register and a set of stickers for your bike only cost 99cents. I have nothing to do with the site but I just communicated with the guys that started it and it seems like they are some programmers with some spare time who love biking.

http://www.bikeregistry.com/