While researching material on background music for videos, podcasts and whatnot, my edjamacation has increased dramatically. Sure, you can get "royalty free" music. But you still have to pay for it; the only thing free is that you don't have to pay royalties. There are several sites that have this kind of music available. The people at "Partners in Rhyme" have some good material. If you want to avoid getting into legal trouble (or having YouTube mistakenly identify music you've uploaded as belonging to someone else, which has happened to me), get the royalty free stuff that you can run with to your heart's content.
They also have some free samples, as well as sound effects. Don't be misled, they are not indicative of the material that you can buy (I almost wanted to start a podcast to tack onto the music!), but there are some gems here that can be pretty good for special projects.