http://labs.echonest.com/SixDegrees/

My mate showed me this website last night and its a interesting time waster.

Put two band names metal/punk/pop in and it tries to find the connection between the two via members or song writers

Some of its quite superficial and it doesn't work with really obscure bands, but you can to funny things like connect Death with Girls Aloud and Eyehategod to Madonna