I don't know about legally downloading for free, but there are many free services out there that allow you to stream music from the web. Some are randomized and others let you choose. Pandora, Spotify, Rhapsody, Rdio, Youtube, and Google Music. Google lets you download in some cases, but most of the their music is pay only with some free stuff thrown here and there. They have a blog(called magnifier?) that showcases new free music. These are the ones I know about. I don't know if this helps any, but I'm new.
