The other day I found out about this new visualization software called VVVV. A company called Meso from Sweden designed it and it's frikkin' wikkid. If you go to vvvv.meso.net you will be pleasantly surprized at this little piece of heaven.
The program it self operates much like puredata or MAX/MSP. If you arn't familiar with those programs, they are visually programming environments to be used for experimenting with and compose music.