Why am I going on about 8-bits games here on TUAW? Because Create Digital Music has discovered a plugin for Garageband that turns your Mac into an 8-bit videogame theme making machine (and really can you think of a better use of your Mac? I didn't think so). Check out the tutorial and leave a link in the comments to any 8-bit tracks you create.
Update: As George points out in the comments this is PowerPC only. Sorry, Intel Mac users.