A good year keeps getting better for Psy: The K-pop star joined Madonna onstage last night at Madison Square Garden in New York to perform his massive hit "Gangnam Style." After promising the audience a surprise, Madonna launched into "Give It 2 Me." Midway through, the song shifted as Psy rose through a trap door and screamed, "Are you ready, NYC?" Wearing a bright red suit, he led Madonna and her dancers through the "Gangnam Style" steps, then stuck around to help out on "Music."