This has to be my personal fav screen saver.
Electric Sheep is a distributed computing project for animating and evolving fractal flames, which are in turn distributed to the networked computers, which display them as a screensaver on the individual node computers of the distributed network. The process is transparent to the casual user, who can simply install the software as a screensaver. Alternatively, the user may become more involved with the project, manually creating sheep (video files of animated fractal flames) for upload to the server.
Check out the project @ www.electricsheep.org