So. Automattic, the company that created and maintains WordPress (which this blog is built upon) also owns a technology called Gravatar.
Basically, Gravatar.com serves up universal avatars to a ton of sites, including this blog. In fact, my current gravatar can be seen in the header, behind the cloud. Also, you'll notice pictures or grey boxes next to comments. Those are all served up by gravatar.
And the cool thing is that you have one account that handles your avatar for every site that uses Gravatar. And the list of sites is growing. WordPress now features gravatars by default in all of their blogging services.
In any case, the service is free, you can link different avatars with different email addresses, and it makes sites look better! So if you don't have a Gravatar yet, click here to get one.