Music Catch is an odd little casual game published by Reflexive. As music plays in the background, multi-colored shapes and notes timed to the music pour out on the screen. The goal is to roll your cursor over as many of the shapes as you can, while avoiding any red shapes.
Music Catch has some built-in music, but it also lets you use any MP3 you want. I pointed it to my Buffy: The Vampire Slayer musical MP3s and played for awhile. It is a strangely captivating game, but gets old very quickly. On the other hand, the registered version is only $9.95 and the idea of music-based games that let the player use his or own MP3s is intriguing even if the execution here is excessively simplistic.