I can't believe this hasn't been mentioned already!
Has anyone heard of / played Audiosurf? If not - and you have $10 to spare and have Steam installed - invest in it. You really really won't regret it.
Audiosurf has the fantastic concept of taking whatever song you chuck at it and making a track/game out of it. The play style is similar to Wipeout, but rather than racing you collect colored blocks which add up to points. Some blocks are worth more than others and your objective is to get the highest score possible by the end of the song.
There are a series of different play styles that you can choose from as well as different difficulty levels. Visually it looks pretty good and runs incredibly smoothly.
All in all, for such a small amount of money it's immensely playable. Since it plays the music you throw at it - you'll enjoy listening to your own tunes throughout - and the accompanying game play is rewarding, frustrating and exciting all at once.
In short, go check it out