It’s called Audiosurf. This has been one of the best used $9 I have ever spent. The game uses your music to create tracks. On these tracks lie a grid that you need to fill with the color blocks. Match the colors of 3 or more to rack up points shown at the top of the screen. At the end of the track the total can be put online in a global rankings system. From there you can compete with others and even friends for the highest score on a music track.
I’ve wasted a better of 5 hours on this game, saying “just one more”. And the best part is that it never seems to get old because every music track is a new game track. And if you have a lot of albums, it goes on forever. It supports every major sound format (No DRM allowed) and it even comes with The Orange Box Soundtrack to start you off. It seems that I’ve been a lot more entertained by cheap $10 games than the traditional $50 game now days.