Spotify - Map shows when two people play same song at same time
Discover on Demand - Just like Spotify's Discover Weekly, but whenever you want.
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
Rocketgraph - Rocketgraph is an open-source drop in replacement to Firebase, except it's much better.
SoundCloud - Enjoy music & follow favourite artists
Pandora - Pandora Radio is a free (ad-supported) internet radio founded in 2000.