If you go to Rockerfelle, go to the "Top of the Rock". It's an observatory they just opened up last year. Great views of NYC on a clear day. It's surrounded by glass so you get an unobstructed view. When I went there was no line, unlike the Empire State building where you have to get up early or else you'll be waiting in line all day.
I like taking the Subway around NYC. Chinatown is a fun place if you want to buy cheap goods.