Well, I guess I should contribute to this thread
I don't download music, but if you are looking to "try before you buy" grooveshark.com is a great place to find new music. While some of it may not be unknown, you can turn on the radio, similar to Pandora, and it will pick songs that are similar to one you selected. You can also make your own playlists, share songs; it's a great place if you love music in general.