Normally I have no screensaver and just have the monitor power down after 20 minutes. However, at the moment I have a bit of a Matrix theme going (4 virtual desktops, a different character wallpaper on each) so I'm using the high resolution Matrix screensaver that came with KDE 3.1.1a - nice and crisp on my 1600x1200 resolution
After I see The Matrix: Reloaded a few times and decide to get rid of my Matrix theme I'll probably switch to the OpenGL screensavers that also came with KDE 3.1.1a - I just discovered them and they're pretty cool.
If I can figure out how to take a screenshot of the screensavers I'll post one.