Tinkersynth - Create and purchase unique generative art
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
Sampulator - Make (and record) beats on your keyboard
Musicroamer - A visual Pandora for discovering new music
Splice Beat Maker - Make and share beats in your browser
stats.fm - With the click of a button you'll be logged with your Spotify account and you'll instantly gain access to a valhalla of cool stats and insights.