19. Gnarls Barkley, "Crazy"
Before "Crazy," Cee Lo Green was a moderately successful solo artist and former member of rap group in tatters. Danger Mouse was a burgeoning indie-rap producer best known for viral mashups. After the surprise international chart success of "Crazy," Cee Lo became a household name and primetime TV star; Danger Mouse now produces best-selling albums for the Black Keys, Beck and, soon, U2.