I've added a classic 88x31 button to the footer of the site. Feel free to copy it to your own site if you want. You can grab it here or at the bottom of any page on my website.
I made it pretty hastily in GIMP, but I don't think it turned out too bad. If you've got a button you'd like me to add to my site, you can contact me. Keep in mind, these buttons must be 88x31 pixels and must be .gifs. They should also be animated or memorable in some way.
This really seems like a cool/fun way to advertise other people's sites. I'm looking forward to seeing everyone elses buttons.