As per Oli's request, I have added Gravatar (Globally Recognized Avatar) support on the forums.
If you have a Gravatar associated with the email account you used to sign up, it should be working now. (If you'd like to override it for this site, just upload an avatar here and it will use that instead.)
If you don't have a Gravatar, and want one, you can sign up at www.gravatar.com
For those without a Gravatar, your default icon will be a cartoon face of some kind. You can also upload your own avatar still if you don't like the default, and don't want to set up a Gravatar account.