Since the software was upgraded, we lost the ability to provide a selection of avatars to choose from. You are now allowed to upload a small image as your 'profile photo' and a resized version of this image will become your avatar. I liked being able to reward contest winners with custom avatars, and having users create new community avatar packs every few years, but there isn't a simple way to reproduce that functionality. If you liked the old avatar images, you can still find them here. Feel free to continue using them.
Don't make me regret turning this feature on. If people start uploading offensive or annoying images, or if people change their avatar too frequently, I'll turn off avatars completely. Ice Nine has his finger poised above the 'suspend' button for anyone with an obnoxious avatar, up to and including album art from bands that he doesn't like.
Edit: People who were previously awarded custom avatars for winning mod/homemade contests will be given small banners under their avatar indicating their award.