Bebo is one of the many social networking websites that is extremely popular in the United Kingdom. It has a large music category that hosts band profiles including several songs that can be played on the site in an embedded player.
The music category lists a multitude of genres to choose from starting with Rock over several kinds of electronic music like Trance and Hardcore to Comedy and Christian music. I honestly do not know most of the bands that have a profile on Bebo making it ideal to find new unknown bands.