Last.fm is a Music community which has infos and sample tracks of nearly all of the artists. Last.fm members can scrobble their listened tracks into their database. So the users can generate a chart for their loved tracks, recent listened tracks, and know about similar artists/songs.
Last.fm also has a nice radio system (which is only unlimited to their subscribed users), which can be started on any kind. Like global tags (like death metal, pop, dance, classical, r&b etc.), Artists (like metall...