This particular site (MusicPlasma.com)has been around for a while now (about 5 years), and I had forgotten about it until recently. The idea is that you enter a band or musician that you like and a word cloud of related/similar bands will appear, those closest being the most closely related, the ones farther out being less similar. Each band cloud can be clicked on to see similar bands to those bands.

They have added movies and actors, but I still find the music the most effective search. Go check it out–it’s worth hours of fun

P.S. On the left-hand side is a link that will link the selected band to Amazon, where you can listen to free sample clips to see if you like the band.