Lately I have been experimenting with Apple's Quartz Composer software, and have found it to be really limitless in its possibilities. I'm still working on getting it to recognize enclosures properly in RSS feeds that it downloads, but everything else has been quite easy and intuitive. Here is a sample of one of the experiments I have been working on that uses microphone input to change the size of a particle generator: .qtz file, .mov file

If you're on a Mac, you should be able to download and open it in quicktime player or as a screensaver.