Okay, aspiring VJs: not happy with the pre-coded solutions out there? Wish you could code your own stuff via a free tool? Check out Processing, a free cross-platform tool. The pay-off: how about 1680×1050 imagery, running at 20-40fps on a lowly PowerBook G4?
Robert Hodgin is featured doing just that, armed with four silver USB knobs (Griffin PowerMates) mounted, glowing blue, on a custom Plexiglass surface. Watch his hypnotic visualizations for GameBoy musician BitShifter, then download the source. More links:
Processing as a VJ tool (project videos, documentation, source, and other info)
Flight404 featuring an insane number of PowerMate tricks
And yes, the master of all things Processing, Chris aka Pixelsumo got to this before I did. Watch his site for regular references to Processing.