Guide to Creative Commons Media for Videographers
I am personally a big proponent behind the idea of the Creative Commons movement, which tries to create a free-er multimedia society where listeners, users and remixers build upon original works and freely exchange that information. The Creative Commons culture features the biggest amount of free music (22,000+ high quality albums), it's easy to find, and they usually have the right license for the job (ported to the legal systems of most countries). In other words, it's your best bet to find a music piece that will fit your video without potential legal consequences.