Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Resolume - Resolume is an application for live video performances.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Veejay - a 'visual' instrument and realtime video sampler
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
LiVES - LiVES is the name of a free and open source video editing software that can be used for performing simple to advanced level of video editing functions.