There are lots of options for free music online. Some of it has commercials, but some don’t. I’ve been listening to some Christmas music on Shoutcast and the commercials are slightly annoying, but not unbearable.

1. Pandora - You type in what you like to listen to and it produces a list of similar artists. One negative is this could keep you from discovering artists you like outside of your typical genres.
2. Shoutcast - Huge selection of music with the occasional commercial. I wouldn’t mind the commercials much except that on SKY.fm, which has some good music, they must have only sold 2 or 3 ads because after a while I could almost quote the ad by heart.
3. 3 Hive - Highlights an album a day and lets you download their music.
4. MP34U - People post songs, you can download them.
5. Magnatune - You can also listen to Magnatune through Shoutcast. The nice thing is they don’t have commercials, but they do have a woman say the album and track and that it’s from Magnatune in a monotonic voice.
6. Remixes - Users can download mixes and add to them.
7. Epitonic - Listen to new releases. You need Flash 8, so Linux users are currently out of luck at the moment.
8. Archive.org - Old music mostly, but not too shabby.
9. Go Ear - Music from various (less-known) artists. The interface only allows you to listen one song at a time.
10. Splice - Music made from short clips of instruments freely available on the site. They have a useful tutorial to show you how to use the site.