Harmonix has developed a Frequency/Amplitude-style game for iPods. Phase: Your Music is the Game uses the touchwheel on your iPod to press on the notes that scroll at you.

A neat little mechanic are some blue notes that you must slide to the appropriate track it is directing to.

The game is worth $5 and has a short tracklist to go with it:

Bang Camaro - Nightlife Commando
Dealership - Dots And Dashes
Freezepop - Pop Music Is Not A Crime
Inter:sect - Midnight Gamma
Kodomo - Spira Mirabilis
Speck - The Theme Of The Awesome
Universal Hall Pass - Dragonfly Remix

Note the Freezepop. =V

The link provided is going to open your iTunes program. If you do not have iTunes installed, it will not function. Or you just don't even have an iPod entirely. =/