Lately it seems to be the in thing to have a cartoon style avatar of yourself. Many are using a service like Faceyourmanga which will create a free avatar based on a variety of physical features you can apply in order to attempt to get it as close as one can to look like themselves. I've seen some really great ones on Twitter.
If your artistic and have some skill with programs like photoshop you can create a very realistic cartoon or caricature of yourself. But if your in the same category I am, I recommend you try one of these sites that do it for you.