Another photo sharing service create by ImageShack with a simple and neat interface.
There's not much to say about these image services, they just need to work, and yfrog does just that -- even better than TwitPic. It gives you shorter URLs, has a better layout, it's more straightforward, you can view pictures in fullscreen, and it has APIs for clients to upload captions the correct way. Absolutely no complaints whatsoever. Almost forgot: better quality uploads *and* it does video. Wins hands down.