Spotify is another great service, that offers the same; free streaming of songs. It downloads as an application, and the stream is of a higher quality: OGG at q5 (160kbps). Better than MP3 at 192kpbs I assure you, like We7 offers. It seems to use a peer to peer network to give the streams at a fast enough pace.
Download it here. I only found it tonight:
http://www.spotify.com