Hey Bill, Just spent a week there this summer. It is on the very top of my favorites list!
I being a history nut can second what others have recommended:
The Yorktown
All the Forts
All the churches
The Old Exchange, Have to see the dungeon where the pirates were kept.
Restaurants, just to name a few, all very good;
*Magnolia's, Favorite
*82 Queen, Favorite
Husk
Library Restaurant
High Cotton
Did I also mention all very expensive!
I really like wondering the back streets in the Battery Park area and along the water front. Just can't say enough about the place and I didn't see everything in a week!