A while back, a fellow by the name of DJ Danger Mouse performed a little experiment. He acquired a vocals-only track of Jay-Z's recent release, the Black Album. He then sampled from the Beatles' White Album to create backing beats, and the Grey Album was born. And it was surprisingly good. It contains some of the best mash-ups I've heard. (My personal favorite is still the Beastie Boys "So Watcha Want" over ODB's "Got Your Money".)
Dj Danger Mouse released it for free on the internet, because it was a derivative work, and he wasn't looking to make money off the track. To him, it was a pure expression of artistic creativity. Unfortunately, word spread a little too fast, and his work recieved a death blow_ a copyright infringement notice, ordering him to take own the music immediately. Unfortunately for the goons over at the RIAA, it was too late. The music had made its way onto P2P networks, and a huge number of websites participated in a 'Grey Tuesday' where they hosted the music. These advocates, and I, believe that his non-commercial use of sampled music to create derivative works was fair use.
This would normally be the part where I launch into a critique of the copyright system in the US, and espouse the awesome possibilities of a system like Creative Commons. Others have already covered this case pretty well, though. Do a search for "Danger Mouse Grey Album", and you'll get about 8 million relevant articles.
So, why am I bringing up this old news, you ask? Well, it's because someone just created a video mash-up of the Beatles and Jay-Z, which is almost as brilliant as the album itself. Check it out, be impressed, and remember that this kind of creative endeavour is an endangered species if copyright law continues down the wrong path.
UPDATE: Waxy has mirrors and a torrent link. Enjoy!