Swift and Mayer's 'Wonderland'

Cowboy boot-wearing cutie Taylor Swift surprised the crowd when she shared the stage with John Mayer during her "Fearless" tour in L.A. OMG!

Taylor, 19, and John, 31, sang his steamy single "Your Body is a Wonderland" for the screaming audience of tweens. Mayer switched to an electric guitar to play along with Swift for "White Horse."

Later that evening, John posted on his Twitter page, "I can't believe the Lakers get to play in the same arena that Taylor Swift performed in!"