Build Your Wild Self is a tool for creating an avatar. You can customize the body parts that you use to make up your "wild self."
Reasonably Clever allows you to create your own Lego avatar. The number of options to customize is near limitless.
Clay Yourself allows you to build a clay avatar.
Gravatar is a tool for creating an avatar that will follow you to any Gravatar supported website. If you post or comment, your Gravatar will appear next to your name.
Doppel Me is a site that you can use to create an avatar of yourself.
Use Voki to create an avatar of yourself. You can then add audio to your custom made avatar.