Visualify - Visualize your top artists on Spotify
Visual Beat - Interactive music video
Spotify Web Visualizer - Beautiful full screen visuals for Spotify web player
Google Music Lab - Interactive experiments that use the Web Audio API
Kaleidosync - Kaleidosync is an all-in-one Spotify music visualizer that is all set to deliver a top-notch music experience with real-time support.
SoundViz - Turn music and sounds into beautiful art