Mr. Fastfinger

If you've got the time and a reasonably-fast connection, you've GOT to go check out Mr. Fastfinger. It was designed by a Finnish programmer/guitar shredmeister named Mika Tyyskä, and he did a KILLER job on it. Take your time and really explore it -- it's a very cool user interface. It's entertaining, it's educational, AND it's extremely fun to totally rock out with some crazy-sick mutant guitar licks, even if you've never played guitar before!