Tauheed Epps has been around since the Nineties, when he was one half of the Southern duo Playaz Circle. But he recently took up the moniker 2 Chainz, and turned into hip-hop's most promiscuous, and hilarious, guest verse-supplier. His commercial solo debut is packed with A-list cameos and producers, but 2 Chainz commands the spotlight – rapping about success and sex with the irrepressible enthusiasm of the upstart he isn't. Occasionally he admits he's been around for a while. But the confession comes with a punch line. Actually, two punch lines: "Former Posturepedic, I was slept on/So many chains it look like my neck gone."

Listen to "Birthday Song":

“I'm Yours”

Jason Mraz re-emerged after his disappointing second album with this lead single, a Jack Johnson-esque ditty about giving yourself fully to someone else. The success of the reggae-tinged song (it earned two Grammy nods and a spot on the Billboard singles chart for well over a year) was something the folk-pop singer never predicted when he wrote it in 15 minutes at home. "I played a happy-hippie chord progression that would probably work without 50 different Bob Marley songs," he told Rolling Stone. "I thought, 'It's too novelty. This is a nursery rhyme,'" concluding that "you can never guess what's gonna be a hit."