Do you like to play some Rock Music?
Try Guitar Geek. That's a nice little Flash game that lets you be a real rock star in front of a virtual audience.
Guitar Geek is like Guitar Hero and similar games. Your job is to play guitar by playing the right notes at the right time. What notes are to be played is indicated on the fret board on the left. Notes are played by pressing the keys A, S, D, and F on the keyboard (so it's actually bass and the game should be called Bass Geek, shoudn't it?). If you miss a note or play it too late or too early you'll lose points and your audience. Try to get all notes in time and your audience will party!
There two things that I don't like in Guitar Geek: First, the number of available songs is quite limited to 5 songs or so. Iincreasing difficulty only gives you more notes to play and more complicated keyboard combinations, but no new songs. Second, playing additional notes is always considered as an error, even if they would be perfectly right at an increased difficulty level.
Nonetheless it's a really cool game. Go ahead and become a Guitar Geek yourself!