Spotify - Map shows when two people play same song at same time
Quod Libet - A extensible Music player with Podcast support, web radio, playlists and many more.
SoundCloud - Enjoy music & follow favourite artists
Amarok - The Amarok team is proud to announce the immediate availability of the result of 2 years of hard work, the beta release of Amarok 2. 9. This release is marked by improvements, corrections and polishing of nearly all Amarok features.
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
MilkDrop - 3D audio visualization plugin, compatible with WinAmp plugin API