Just got back myself,..put one day aside for Metropolitain Museum of Art (Central Park East) that was fantastic, the Guggenheim was a let down,only half the museum was open, so don't bother with that. Try a helicopter ride ober Manhattan(about $100 for 10 minutes.
- well worth it. (book in advance)
Take a walk around the less touristy places like Hell Kitchen, most of the old rough charm has gone, but you still get to see how the other half lives(blocks between west35-west55 streets )
Enjoy!