The Grey Album

The Grey Album is a musical mash-up by the artist Danger Mouse that combines songs from The Beatles' White Album and the vocal tracks from Jay-Z's The Black Album. The backing tracks from the White Album are cut up, sped up, and reconstructed to match the flow of Jay-Z's vocals, resulting in songs that sound very little like the originals despite being completely composed of samples from them. 

Here is The Beatles version of Helter Skelter

And here is Jay-Z's 99 Problems

And here is the Grey Album Version

The Grey Album created a fair amount of controversy when it was released due to the presence of the Beatles tracks. EMI, which owns the rights to The White Album, wrote cease and desist letters to stop any kind of distribution. This led to a day long protest where over a hundred websites encouraged people to download the album. 

From Wikipedia,

"Grey Tuesday was a day of coordinated electronic civil disobediance on February 24, 2004. Led by Downhill Battle, an activist group seeking to restructure the music industry, participating websites posted copies of Danger Mouse's The Grey Album for free download on its sites for 24 hours in protest of EMI's attempts to prevent any distribution of this unlicensed work. This protest was provoked by the opinion that the sampling is fair use and that a statutory license should be provided in the same manner as if a song had been covered. Hundreds of web sites participated and roughly 170 hosted the album for download. Over 100,000 copies were downloaded on that day alone. The legal repercussions of the protest were minimal; a number of the participants received cease and desist letters from EMI, but no charges were filed in connection with the event."