There's nothing like shooting a low-budget video and scoring it with some recognizable music. Most sites aren't preventing amateurs from using copyrighted music, but this will become a bigger issue in the months ahead…. especially if you're making income on your videos on sites like Revver.com.
In the meantime, you have four choices:
1) Go to a free, royalty free site like Podsafe. It's easy to use, but you have to sort through a lot to find the tune you'll need.
2) You can create your music using tools like GarageBand (free with a Mac). It's easy to use but your video will sound like everyone elses.
3) Find someone you know that scores music (tough one for most of us). You'd probably want to give them credit and give them a piece of your income.
4) You can buy royalty-free music, but it's usually priced high ($100-$200 for a CD) for professionals. I haven't found a low-cost site ($1-$3 a tune) for really polished royalty-free tunes. If you know of one, let us know!