Justin Bieber + Friends: Ludacris

Justin Bieber and Ludacris are both pals and collaborators. Luda contributed the rap to the infectious breakout single 'Baby,' telling about his first love: "She woke me up daily / Don't need no Starbucks."

Strangely but not surprisingly, the inescapable hit about one's first broken heart garnered the duo an insane amount of love. Go figure!