I have a subscription MusicMatch's "On Demand" service, which includes the ability to put in an artist and say "Music like this." I loved this when I first experienced it, but Pandora is much better.
Compare these two results for a seed of "Jesus & Mary Chain":
MusicMatch "Artist Match"
- "Situation" by Yaz
- "Blue Monday" by New Order
- "Love & Peace or Else" by U2
- "Some Girls Are Bigger Than Others" by The Smiths
- "Cities" by The Talking Heads
Okay, fair enough recreation of a 1982 New Wave commercial radio playlist...
- "Eric's Trip" by Sonic Youth
- "Stand Guard" by Bob Mould
- "Pig Knuckled Clown" by Flour
- "Sometimes" by Firehose
- "Soft Signals" by Limblifter
Now that's like what you'd expect from a college DJ! With Pandora, you can actually fine-tune what you want to hear considerably, but even with just the seed there's no question that Pandora "gets" the sound of Jesus & Mary Chain and MusicMatch "gets" the era and that its "New Wave."
Between KEXP.ORG, ReplayRadio, MusicMatch On Demand, and Pandora, I actually feel like I'm hearing as much musical diversity as I ever did on the mainland.