Two people suggested Pandora to me in the past 24 hours. It’s from the creators of the Music Genome Project. You create a radio station based on things that you like (e.g. I’m listening to the Pink Floyd Station right now) and it find music you’ll like. You give it feedback, and it adjusts its recommendations. It harkens back to Agents Inc (Firefly) from the mid-1990’s, but in addition to recommendations, actually streams the music and lets you buy the song from iTunes or the album from Amazon. Very cool.