Fine, fresh, fierce, she's got it on lock: Katy Perry's California Gurls is the top song of the summer. According to Billboard, Perry's groove with Snoop Dogg is the summer's No. 1 tune. It seems to have been the season for collaborations: Eminem and Rihanna are second with Love the Way You Lie, followed by B.o.B and Hayley Williams with Airplanes. Usher and will.i.am's club hit OMG is fourth, Taio Cruz comes in fifth with Dynamite, and Travie McCoy and Bruno Mars' reggae-tinged Billionaire snags sixth. Mike Posner's Cooler Than Me is seventh, Enrique Iglesias and Pitbull score eighth with party song I Like It, and Drake comes in ninth with Find Your Love. Eminem is the only artist on the list twice. He's also at No. 10 with Not Afraid.