"Creative Commons" for copyright free music

The use of copyrighted music on your showreel is a widely debated topic and something we all should be considering. This was less of a consideration in the past as only a handfull of potential employers would ever be viewing the reel but now that everyone's reel is appearing online with a potential audience of millions it is something to consider carefully.
Of course the ideal would be to record your own music, or have a friend record or allow use of an original piece of their own.
This isn't always possible. It would be great if we could just use our favorite song and not worry about copyright. after all it's only going to be a minute or two right?
Well technically anything over 30 seconds you are legally obliged to either get permission for or pay to use. Many record labels, especially minor, independent ones will often be very approachable and forthcoming with permission to use one of their tracks for a student showreel providing you ask nice!
Many people still go ahead and use tracks from major bands on major labels on their reels without permission thinking "what's the worst that can happen?" in most cases your reel may get pulled from whatever site was hosting it or you get a cease and desist notice.
There are other options such as using copyright free material, or "creative commons" material... http://creativecommons.org/ You can do a search for a particular genre of music then listen to and download appropriate tracks.