Spotify - Map shows when two people play same song at same time
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
SoundCloud - Enjoy music & follow favourite artists
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.