Another Arduino project at Makezine:
6-pack - Arduino-based controller for live audio/video performances
"6-pack is an open-ended, highly customisable, and ultra-portable physical controller based on the Arduino board. 6-pack is an Arduino shield consisting of 6 linear potentiometer sliders that can be assigned to different variables in the user's preferred software. It can be used to control a wide array of audio/video applications, from software synthesizers to HDJ systems. All, with a minimal footprint (3,5" x 2,5") and on the cheap (just a fraction of the cost of an equivalent MIDI interface). The project is open source. Schematics and source code included."