Its called AudioSurf, and its having a free beta weekend today and tomorrow. Unlike guitar hero or other rhythm games you can use all your own songs to play, here someone is playing it to the futurama theme song. I’ve been hooked on this for the past several hours, it works really well with any song but im enjoying it with classical music the best right now. You can download it here.
This is very, very cool. The roller-coaster track is a trip and makes it incredibly entertaining.
I’m having a bit of a time figuring out which songs would be most amusing. I picked Metallica right off the bat hoping it would kick ass and found it was rather ho-hum. So far the best have been: Back in Black (AC/DC), Stray Cat Strut (Stray Cats), Sabotage (Beastie Boys), and Angst in my Pants (The Sparks).
I thought at first anything with a strong drumbeat would be best but Prodigy was rather boring. I think it’s rather picking up on the peaks and valleys in the waveform, so anything that’s been compressed is going to not have a very intense track.
Which difficulty are you playing on? anything on the first level is going to be really slow.
Beta expired 
Have to catch it next time, it seems fun.
I’m only playing on the easiest setting, mostly because I’m having a hard time not zoning out on the background. 