Two links to some really good music.
The two links are to Minnesota Public Radio, which pretty much plays classical music 24-7. It's a great way to expose yourself to classical music you've never heard before. And when you hear a piece you really like, you can go out and get it. That way you'll only get music you like. So here's Minnesota Public Radio. From this link, near the top under Classical, you'll see a link called Listen with a little speaker. Click that link. A little popup will come up (you need to enable popups). I recommend the mp3 128k stream. Click that link, and RealPlayer should play that stream for you.
The second link is to the BBC Radio. They have several radio stations that are worthwhile, but I like Radio 3. You can get there here. From this screen, hit BBC Radio 3 right in the middle of the screen. Then, on the left-hand side of the screen, hit the link for classical. From there, on the right-hand side of the screen, you can pick lots of great things. One of the most popular (and I like it very much as well) is Choral Evensong. You hit the little speaker symbol, and a popup comes up with some controls and information. Important: Choral Evensong is updated once a week on Wednesday. So if you listen to it twice (certainly no crime), you'll get the same program until after Wednesday.