Gravatar support has been added to this site. Short for Globally Recognised AVATAR, it lets you use the same avatar in lots of different places. You'll notice it in the form of my avatar next to posts, and your's next to your comments. Just head over to their site, sign up, upload your avatar, and you're set.
I don't know what happens if you have a Gravatar, but don't have an account here. Maybe it still shows yours anyway?