58. Danger Mouse, 'The Grey Album'
The mash-up reached a conceptual and artistic plateau with Danger Mouse's fusion of The Beatles' White Album and Jay-Z's Black Album. It sounded like a stunt ("Justify My Thug" meets "Rocky Racoon"?) but it was really a love letter – a music geek's mash-note to hop-hop and classic rock – and a polemic: an argument that the best hip-hop warrants a place alongside the most revered gods of the pop music canon. But it was the sheer musicality of the thing that carried the day: Who knew that "Dirt Off Your Shoulder" and "Julia" could get along so beautifully?