50. Outkast, "B.O.B."
Outkast greeted the 21st century with a single that'll probably sound ahead of its time in the 22nd. Big Boi and André 3000 were inspired by hearing the hard, double-time rhythms of drum-and-bass music at a London party. "There wasn't anything in hip-hop that was killing me at the time," André said. "But that shit was tough … I thought about how to Americanize it." With an insane beat, Hendrix-at-Monterey guitar and massed voices chanting like a gospel choir conducted by Afrika Bambaataa, "B.O.B." became one of the greatest left-field hits of all time.