MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Visualify - Visualize your top artists on Spotify
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Spotify Web Visualizer - Beautiful full screen visuals for Spotify web player
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Graphic Foundry - High-impact audio reactive music visualizers 💎