Spotify: Ad-Supported Music Sharing in Sweden
Spotify (still currently in invitation-only beta) is a new Swedish service that lets users listen to the music they want, when they want. They simply have to download and install the free software and they can start enjoying instantly. There are no restrictions in terms of what you can listen to or when because Spotify has cleared the rights to the music.
Spotify operates under the belief that music is social, so it was designed to allow users to share songs and playlists with their friends and even work together on collaborative playlists. The site is a free service financed through advertising. (Naturally, there are also a variety of flexible subscription options, for example, a premium account which lets you skip the ads.)