Consider some of these sites…
http://audioblocks.com/ — Thousands of sound effects and great background tracks. A membership allows unlimited downloads.
http://www.freestockmusic.com/ — Like the name says, it’s completely free and they have tons of choices.
http://freemusicarchive.org/ — You can search by artist or category and it’s all free.
http://freeplaymusic.com/ — Thousands of tunes, royalty free for non-profit or personal use. Commercial productions have to pay royalties.