I think I campaigned for 50x50 (as that's what dA uses, and it's also a nice size to resize my 100x100 ones for yahoo/msn/lj to), but apparently 48x48 is just as common. That makes it 3 sets of images for avatars then.

I like them being small, anyway. It's a lot nicer than the great big signature images people used to have, especially when you have a tempermental 48k-on-a-good-day dialup connection.