The iTunes Store always has some free tracks and TV shows. Fairly recently (maybe I didn’t notice it before) they added a page where users can see all the free content. That’s convenient.
Direct Link (U.S. store).
Actually, with two free tracks a week on the U.S. store and one free track a week on the Canada store, I’ve been able to find a few interesting songs.
Of course, those tracks and TV shows are still protected with the FairPlay DRM, which has negative consequences. But it’s still cool to have a few things to play with.
Other sites, including CalabashMusic, also have free music, usually without any DRM copy-protection. The advantages of iTunes have mostly to do with the integration between the store, the software, and iPods, but these other stores are well worth checking out.