An ongoing music recommendation database - "Last.fm" (once known as "Audioscrobbler") offers media player plugins to its users. These plugins, which can be installed onto iTunes, Winamp and others, will monitor and record the ID3 data of any MP3 played by that media player. This is uploaded to a large database, which finds other users who have played the same tracks and recommends you new musical artists based on their databases. You can even download the Last.fm Player and listen to sample songs by your recommended bands. I have used this service since September of 2005, and it has never ceased to be a source of new music for me.