projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Otter Live Notes - Record, transcribe, and take live notes on podcasts & videos
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.
VJmachine - Music Visualizer - Make a VJ show like a PRO. Music visualizer for a unique tight symbiosis of sound and video.
Plane9 - Plane9 is a revolutionary 3d visualizer where you never have to settle for just one view ever again.