Last week I began using Last.fm to stream a variety of music to my computer for free. The quality is great, and the site tailors a playlist for the user based on the music he/she listens to. Lately I have been listening to a lot of film scores (like Harry Gregson-Williams' stuff) and some pretty sub-genre specific metal and have been pleased with a lot of what they offer. If I don't like a song, I can just skip past it to their next offering. That is awesome. Actually, any track can be banned (don't play again), loved, or just skipped. Each track that gets a full play is noted by Last.fm and a database is kept of the music you like. The music player is lightweight, downloads quickly and has been running flawlessly for me.
From the site:
You get your own online music profile that you can fill up with the music you like. This information is used to create a personal radio station and to find users who are similar to you. Last.fm can even play you new artists and songs you might like. It's addictive, it's growing, it's free, it's music.
Your best bet is to go to the website, get hooked up and give it a try. Anyone else playing with this?