Audiosurf is a game that takes any audio file and turns it into a a rhythm game. Several different modes are included as well as multiplayer. The game is like solving a color matching puzzle while driving a car on a road made of music. In other words, it's actually fun instead of just doing what the game tells you.
http://www.gametrailers.com/player/usermovies/160659.html That's some gameplay of one of the modes. Normally, the game goes online so that if you ever play a song, you can find out who got the highest scores for it but it's down right now. As long as the audio file is under 25 minutes, it will work. It's still in Beta so it can't go online right now.
(This is the game.)
http://rs66.rapidshare.com/files/84810688/AudioSurf.rar
(This is what's needed to play it offline.)
http://www.mediafire.com/?2jjjx4xdvd1
There is some technical stuff you have to do first though so don't install like crazy just yet. The directions should be included in the second link.