I fell in love with Tiger's RSS Screensaver as soon as I saw it, but the fact that it couldn't use more than one feed at once annoyed me - why could I not get the latest headlines from the BBC and MacOSXHints, for example, on the same saver?
So, not one to give up easily, I wrote a script in PHP called FEEDcombine that automatically combines RSS feeds into one 'metafeed.' You just select the feeds you want from the predefined options (or enter your own as an alternative), choose how many entries from each feed you want, and click "Generate." Finally, bookmark the page which comes up in Safari. And there you go -- multiple feeds in the one screensaver.
Remember, the screensaver will only show up to 10 items -- so if you've got multiple feeds, don't set the number of entries from each feed too high, or entries from the later feeds won't come up.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050516081636903