Here is a great site for downloading free kids music! I downloaded each traditional title and then burned them all to a CD... now we have car music!
Traditional Childrens Songs | Children Songs.
We also have DISH Network, and enjoy listening to channel 976 - Kids' Music. I'm sure every cable/satellite provider probably has something comparable. It's often on when we're in the living room and she enjoys dancing to it. Just be aware - TVs suck a lot of energy, so turn off when not in use!
If anyone has recommendations for other sources of free kids' music, please post!