So here is my top 5:
1: Westport CT
Get out of New York for just one day to have a completely different experience.
Take the train from NY Central Station to South Norwalk. The train ride takes 1 hour. From there it's a 15 minute drive to Compo Beach in Westport. Have a walk along the beach and enjoy the view and the beautiful houses. Then go back to the center of Westport for some shopping (10 minute drive). Lovely boutiques from Calypso, Kate Spade, Tiffany's & Co and William Sonoma. Have lunch at The Tavern on Main Street. For dinner there are excellent restaurants in South Norwalk.
Rent a bike (for instance at Blazing Saddles on Pier 78). Follow the Bike lane on the Hudson River Side and go south. Cross over to the other side through Warren Street (just follow the bike signs) and go over the Brooklyn Bridge. A magnificent experience with spectacular views. You can expand your biking trip by going through Brooklyn a bit and then go back over the Brooklyn bridge again. You could take the Manhattan bridge, but the Brooklyn Bridge is really something special and worth the double trip. Then go all the way down on Manhattan. Stop at St. Paul's Chapel and go in to see this memorial place of 9/11. Really impressive and a must do!
Then continue south towards Battery Park. You could park the bikes here and take the free Staten Island Ferry for a great view on the Statue of Liberty. Then continue along the hudson river side. This is the best bit of the trip. Truely fantastic to be biking on the promenade.having the river on your left side and the view on skyscrapers on the right.
3: St Paul's Chapel
This place is definitely worth a visitor because of it's essential role in the 9-11 recovery works. It was a safe haven for all the fire fighters, police, construction workers and other people that were working around the clock on recovery work. A place for eating, sleeping and peace. Now it's turned into a memorial place showing the solidarity of people around the world.
4: Highline Park
The High Line is located on Manhattan's West Side. It runs from Gansevoort Street in the Meatpacking District to West 34th Street, between 10th & 11th Avenues. The first section of the High Line opened on June 9, 2009. It runs from Gansevoort Street to West 20th Street. The second section, which runs between West 20th and West 30th Streets, opened June 8, 2011. It's a great place to take a step back from the huge buildings and traffic and enjoy some quiet. After having walked on the high line go to Pastis for a nice French lunch.
5: Top of the Rock
Although very touristic, this is an excellent place to view the city from the 70th floor. Go at the end of the day, just when the lights start to show. You will have a great view on Manhattan, showing Central Park on one side and the Empire State Building and Time Square on the other (The Empoire State building really is beautiful and a shame you can't see it when you go up there for a view). Top of the Rock is on top of the GE building (part of Rockefeller center) and reopened in 2005. Tickets are $25 or adults and $16 for kids (6-12 years). When you finish your visit, don't forget to also have a look at the Ice Rink in the Rockefeller center and you may even want to do some ice skating yourself.
Final shopping tips
Of course you can do plenty of shopping in New York. There are huge department stores, like Macy's and Bloomingdales. We actually found these a bit disappointing. Not like Harvey Nichols or Harrods. Anyway there are three shops I think you shouldn't miss:
1: Kate Spade New York, a brand that combines playfulness with elegance. I think the shop in Soho is probably the best (Broome street).
2: Calypso St. Barth, a lovely shop for elegant cashmere and comfortable but feminine clothing. Also to be found in Soho (Broome street) and meatpacking district (Hudson street). And also in Westport.
3: Magnolia's Bakery, for the excellent cupcakes. Just enjoy the soft and creamy taste of the cupcakes. There are several locations in the city. We had our cakes from the store on the corner of the Rockefeller centre.
4. American Girl Store, the place to go if you have girls up to 12 years old. New York girls have birthday parties here and they take their dolls for a haircut, a new hairdo or an new outfit. Excellent toy concept by Mattel. On 5the avenue near Rockefeller center (that's why you'll see girls with dolls in the ice rink)
5. William Sonoma for amateur cooks. Just love this shops with all the cookware and tableware. Now also shipping to Europe... (on 7th Av/16th street) and in Westport.