Pandora Radio. Its a program that as an amateur musician I've used for a few years now. Its simple, you type in a favorite song or band and it finds you listings based on your preferences. The more you add to it by using the "add variety button" the more of the music You like comes up. I've found plenty of songs to cover using this program and honestly I'd rather use Pandora than pay for Itunes.
Type in John Mayer, get Jack Johnson.
Type in Smashing Pumpkins and you get Green Day.
Really anything you can think of will come out and reveal to you a whole new world of music! Begin by going to the site (pandora.net), make a account (takes maybe two minutes, email, password, blah blah blah), and fill in the band name. You can favorite songs, artists, and albums. You can hit dislike and never listen to it on that station again. Make a station for easy listening, classical music, punk rock, pop, classic rock, j-rock, anything really and you have all you need. I think a paid membership relieves you of ads breaking up the list (don't quote me on that) so thats the only downside. The ads. I think I've heard the same commercial for Hardee's for a month now.
Overall I think its a great free site.