Here's a neat little find.
I was just browsing around for avatar ideas (you can never have too many great avatars), and found
http://www.animegalleries.net/.
They've got a whole bunch of anime pictures. But here's the neat part. They've got a Javascript feature that lets you resize and crop the pictures down to produce avatar-sized pictures (100x100, 64x64, whatever size you want).
You can get better-looking results with a photo editing program, but I guess if you don't want to install anything, and are too shy to ask someone else to crop the pics, then this is for you.