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