Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
MadMapper - The Mapping Software
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Resolume - Resolume is an application for live video performances.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Linux Show Player - Sound player designed for stage productions