MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Fliqlo Screensaver - A screensaver that displays the time using a flip clock.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Padbury Clock Screensaver - Minimal screensaver for Mac
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Xscreensaver for Windows - XScreenSaverWin is a Windows port of XScreenSaver. 204 screensavers in XScreenSaver were ported.