KATY PERRY & SNOOP DOGG
One of the songs of summer, this No. 1 smash shows that the Doggfather can add gangsta flavor to even the most sugary of dance-pop confections.
EMINEM & RIHANNA
"LOVE THE WAY YOU LIE"
Ri-Ri-who also scored a No. 1 hit with Drake ("What's My Name?") in 2010-perfectly tempers Em's toughness with her tenderness.
B.O.B & BRUNO MARS
"NOTHIN' ON YOU"
These two dudes weren't afraid to get mushy with a declaration of devotion that won us all over.
LADY GAGA & Beyoncé Knowles
Not since Barbra Streisand and Donna Summer teamed up on 1979's "No More Tears (Enough Is Enough)" have we seen a divalicious duet like this!
USHER & WILL.I.AM
Sure, it sounds like a Black Eyed Peas song-and Usher doesn't need to use Auto-Tune-but it still had us all going, "Oh my gosh!"