Visualify - Visualize your top artists on Spotify
Sampulator - Make (and record) beats on your keyboard
Spotify Web Visualizer - Beautiful full screen visuals for Spotify web player
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Synesthesia - Synesthesia is a Spotify music visualizer that comes with the advanced support to listen to thousands of music tracks with the visuals side by side.
Ramsophone - A generative art/music machine. (Be sure to refresh!)