Fun was definitely on the menu for the '2011 American Music Awards' (Sun., 8PM ET on ABC). The night was absolutely packed with memorable performances and surprise guest stars. Fighting Gravity went unannounced, but certainly helped make the debut of will.i.am's collaboration with Jennifer Lopez on 'T.H.E. (The Hardest Ever)' one of the most memorable of the night.

Other surprise appearances included a couple of guests who crashed the party at the end of the night with LMFAO performing their two hits. First, Justin Bieber broke out his dance moves on 'Party Rock Anthem,' and then David Hasselhoff joined the boys and Quest Crew to shake his moneymaker on 'Sexy and I Know It.'