I'm so excited for you Dawn! You'll absolutely love it here, it's the best! Just make sure you make a list of what you want to do most, because it'll be hard to fit it all in during one weekend. You usually need at least half-a-day each for both Central Park and the MET, both are gorgeous and HUGE! And by the time you get down to Ground Zero, check out the sites, and take a boat out to the Statue of Liberty and Ellis Island, that's almost a full-day outing.
And just be prepared for MOMA. While the MET's full of gorgeous works of art from around the world, Egyptian tombs you can walk through, and period houses, MOMA's a lot more offbeat. It's definitely an experience! We went again this past summer and there were a few installation exhibits that were cool, but then there were rooms full of completely blank canvases that people stood there staring it. It was hilarious! There was also video of a naked woman hula-hooping with barbed wire and it was beyond disturbing. It's a unique place but just be prepared!
Have you gotten your Wicked tickets yet? It's one of the few shows that are still doing really well despite the economic downfall, and it usually sells out months in advance. If you want good seats, make sure you get tickets ASAP!
You're definitely doing the right thing by going to the Top of the Rock instead of the Empire State Building. The ESB's nice, but Top of the Rock is much better! My friends and I go a lot since my dad works in the building and gets us the NBC employee discount, and it's SO much fun! The elevator ride to the top of the building is an experience in and of itself. I have some video I may upload to show you later! Plus the views are unparalleled.... you get a great view of the city, the Empire State Building across the way, and all of Central Park. It's beautiful!
And don't forget about Toys'R'Us Times Square! I know a lot of people don't think about visiting Toys R Us on their vacations, but it's officially the biggest toy store in the world and it's so much fun! You can go on a huge ferris wheel, walk through a life-sized Barbie Dream House, and see animatronic dinosaurs and superheroes. It's really cute in there!
Sardis is great but I'd honestly skip Serendipity III. They have good chocolate, but when we went two summers ago we were greeted by some rat friends

The place has been shut down twice already, after repeatedly failing inspections by the Board of Health for being filthy. I know people love it, but it completely skeeves me out. Plus the customer service SUCKS. They cram as many people as they can into a tiny dump of a room, and they don't offer to-go boxes. If you don't finish your food they don't want you taking it with you. The manager is a piece of work, too, who chargers over-the-top prices and then doesn't care about your experience or food once they have your money. I'd stay away, it's way overrated and there are so many better restaurants to try! If you're looking for a fun experience, Ellen's Stardust Diner is so much fun! It's right there on Broadway and set up to look like an old 50's diner. 50's musicals play on a big screen in the center of the restaurant, and all the waiters and waitresses either were or are on Broadway, and they sing as they bring you your food. The food's delicious too, and you get so much of it! It's not the most authentic experience if you're looking for fine dining, but it's definitely authentically New York!
I'd also put Madame Tussaud's last on your list. Between the sightseeing, museums, attractions, shopping and ethnic neighborhoods (don't miss the West Village either, they have the BEST stores!), you won't have time to do everything and the place is a ripoff. It's fun if you have extra time, but they charge an insane amount of money to take pictures by statues that you can see at any other Madame Tussauds. If you have extra time, I'd do the NBC Studio Tour to see some actual celebrities rehearsing for SNL!
OK, I just wrote you a book

I'm so excited that you're finally getting to see the city! Keep us updated on your plans!