I use the default Window XP where the whole screen is blank/black and there is the Windows XP words popping up randomly. Oh, and I didn't like those pop-ups from that link. There was one that stuck to the middle of the screen so I couldn't read the welcome message. Oh well.
I use the "Alias" screen saver for the Alias tv show, it has these hexagon shapes, honeycomb type shapes coming into few and fading away, it is pretty cool.