Playlist Machinery - Tools that help you create & organize your Spotify playlists
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
TrackStack - Easy Spotify playlist sharing and collaboration
Spotify - Map shows when two people play same song at same time
BeatMix - Enables Shuffle and Radio for multiple artists in Spotify
TuneIn Radio - With TuneIn Radio Mobile, your mobile device becomes the radio.