I've been using Pandora for a while now. It's a Internet radio station where you create your own stations. When you start you enter an artist or a song or something and it then tries to play songs that are similar to that one you entered. So, I enter "Frank Zappa" and now it's playing songs that sound like Frank Zappa songs (and some Frank Zappa too of course). Songs do repeat I must admit, but it's not very often. It's not a free service like so many other Internet radio stations but unlike others, on this one you can fast forward. If there's a song you don't like, you click the little album icon that is shown and select "I don't like it". This skips that song and I hope to believe it remembers this and doesn't try to play that song again in a long time.
Likewise, if there's a song you like, you click and say "I like it" which just means it'll be played again fairly soon.
The price is really cheap too. It's $36 for a year or $12 for a quarter. If you want to you can try it for free for 10 hours which is what I did and was impressed enough to pay up. I really recommend this site to all readers of this page.
Another neat thing is that if there's a song you really like you can click the icon and select to buy it from iTunes or Amazon. (unfortunately Amazon.com and not Amazon.co.uk) So far, by discovering good songs on Pandora I've purchased two CDs from Amazon.