MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Jokosher - Jokosher is a simple and powerful multi-track studio.
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Fission - Edit audio in minutes, not hours.
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
MusicBoard - Mb Launchpad is the first Linux launchpad.