Bandcamp - Discover amazing music and directly support the artists who make it.
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
SoundCloud - Enjoy music & follow favourite artists
Hype Machine - Hype Machine lets music fans discover artists. Its technology scrapes audio files from diverse music blogs and posts them to the website. Users can peruse the site or sign up for Hype Machine's newsletter for updates.
Pandora - Pandora Radio is a free (ad-supported) internet radio founded in 2000.
Spotify - Map shows when two people play same song at same time