Bocho came up with a really neat controller for RGB LED strips. The idea is to compliment a VJ performance, full of knobs and sliders of course. Something that you can tweak in real time, but can also be assisted by the music. Bocho started out with this post on bass detection on Arduino, which was then rolled into the controller.
The build uses 3 high power transistors for controlling current, and various pots and sliders that control oscillation speed, luminosity, hue, and selecting manual or beat detection all controlled by an Arduino. Even better the project is wrapped in a decent looking enclosure.