The Met, The Guggenheim, 9/11 Memorial / Freedom Tower, Statue of Liberty/Ellis Island. The Central Park Zoo is a nice walk-thru.
Hungry? Then you'd better eat at Carmine's in Times Square, which is an incredible Italian eatery with family style (large plates to pass around your table) serving.
Honestly, I've been to NYC plenty of times as I only live 3 hours away. NYC is NOT my favourite US city. I'd much rather visit the much more interesting Chicago, Washington DC, etc.