Years ago when I was working on a photo gallery for davedash.com I got the art of making tumbnails down fairly well. It was automated and didn't allow for specifying how the thumbnail should be made. With dozens of photos (which was a lot back then), when would I find that kind of time.

Flashback to today, for my company... we want users with avatars... but nothing too large. Maybe a nice 80x80 picture. Well the coolest UI I've seen was Apple's Address Book which let you use this slider mechanism to crop a fixed sized image from a larger image.

They create a pretty slick little app, using symfony to handle the framework for the app, some Javascript in the form of Prototype to make the controls, and plenty of CSS/HTML to make it usable. You can check out the demo here.