From those lovely people at snowHeads:

• Empire State Building: it might look as though there are no queues, but the queue after the cashier snakes a hell of a long way. The whole visit, including queuing took about 2.5 hours. Went to the top of the Rockerfeller Centre in the evening - takes about an hour and fab for seeing NYC lit up - and you get a better view of the Chrysler Building and see the top of the Empire State lit up.
• Helicopter Flight: best 1st thing in the morning (you will be awake anyway). Recommend Liberty.
• Statue of Liberty: If you want to visit then fine, but allow plenty of time for queuing/travel ont he ferry. If you just want to see, then helicopter is the way.
• Abercrombie & Fitch: (if you have to buy for teenagers), best 3/4 hour before closing, otherwise queue to get in
• Metropolitan Museum: Target what you want to see and don’t be tempted to stray - you’ll be in there all day.
• Grand Cental Station: Just to see it.
• The subway is your friend; yellow cabs are your friend if you hail a cab going in the right direction.
• If you go to Macy’s, Bloomingdales etc go directly to customer services for your 11% discount card (no sales tax on clothing in NYC)
• Radio City Music Hall backstage tour if you like Art Deco
• Get “On the Town” out on DVD
• What about renting bikes in Central Park? That’s what we plan to do and I see they rent them out from one hour at $20
• …have lunch in the Oyster Bar in GC Station and take the Staten Island ferry (and come back on it); gives you a great view of Manhattan as well as the SofL. Agree about the helicopter flight; we took one at dusk, whcih seemed like a good time.