Visualify - Visualize your top artists on Spotify
Google Music Lab - Interactive experiments that use the Web Audio API
SYQEL - Bring your music to life
Splice Beat Maker - Make and share beats in your browser
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.
108 - A minimal beat machine played in the browser.