MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
JWildfire - Modern ui, soft developed and ugraded by andreas maschke for design 2d and 3d fractal flames. Very nice app and powerful.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Apophysis - Apophysis is a fractal flame editor and renderer for Microsoft Windows.
VJmachine - Music Visualizer - Make a VJ show like a PRO. Music visualizer for a unique tight symbiosis of sound and video.
Electric Sheep - Electric Sheep is a collaborative abstract artwork founded by Scott Draves.