You should check out Moby's (huge) collection of music that he WANTS you to use...
Watch the vid below to find out more about it...
Googling will help you find many more resources of royalty free music.
Here is a link where you can check whether or not it's legitimate to use some other copyrighted music with your film.
My brother makes royalty free music -- and if you'd like to use something from his library -- stock20.com -- I could probably get you a good deal!
