Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
QLab - QLab, Live show control for Mac OS X.
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Cue Player - Cue Player software for theater sound and lighting
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
MadMapper - The Mapping Software