I made a couple of neat looking "screensavers" using Quartz Composer on my Mac. These use the iSight camera built into most recent Macs for part of the pattern. They also use An RSS headline feed from BBC world news. The teapot version certainly won't save your CRT from "burn-in" and they use a fair amount of system resources. Since LCDs don't burn in this may not be an obstacle to using them to amaze your friends. Put them in an appropriate folder like /Library/Screen Savers.
The camera cannot be used by two applications at the same time so you may need to quit another application in order to see these screen savers properly. You should be able to edit these screen savers to alter the graphics or the RSS feed with Quartz Composer which is included with the free developer tools from Apple.