Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
You should be able to use quartz composer files as background too 🙂

So say for example there is a .qtz screensaver or file from sites like quartzcompositions.com, you can drag those just like movie files and get interesting animated background 🙂
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.