MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Visualify - Visualize your top artists on Spotify
Amarok - The Amarok team is proud to announce the immediate availability of the result of 2 years of hard work, the beta release of Amarok 2. 9. This release is marked by improvements, corrections and polishing of nearly all Amarok features.
Spotify Web Visualizer - Beautiful full screen visuals for Spotify web player
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Graphic Foundry - High-impact audio reactive music visualizers 💎