I know this was on here at Steam some time ago (3 months or so) and was cheaper but this is now the cheapest i can find delivered plus a few pence off with Quidco, usually dispatched in 2-4 weeks though, but still a great deal,
Ride your music.
Audiosurf is a music-adapting puzzle racer where you use your own music to create your own experience. The shape, the speed, and the mood of each ride is determined by the song you choose. You earn points for clustering together blocks of the same color on the highway, and compete with others on the internet for the high score on your favorite songs.
Play with any music from your own collection--the game supports MP3s, iTunes M4As, WMAs, CDs and OGGs
Online scoreboards for each song you play.
Choose your strategy from 14 available characters