I took my teenage boys there for 2 days and we had a blast! I disagree that it has to be expensive. Some of the best things we did were completely free:
All free:
*Staten Island Ferry----goes around Statue of Liberty & Ellis Island
*Apple flagship store--free calls and can play with everything
*FAO Schwartz
*Toys R Us flagship store (they preferred over FAO)
*911 Museum and St. Johns(?) church (took care of all the 9-11 volunteers; it's just across the street), both devoted to 9-11...very interesting
*St. Patrick's Cathedral and gift shop--beautiful--they spent at least an hour here
*NY Library (look up the right branch, I can't remember) --houses the real Pooh stuffed animals
*Natural History Museum--actually free, don't HAVE to pay
*Times Square--so much to see, very festive
*Chinatown, Little Italy
We splurged on the Blue Man Group, and got front row seats. It's off-broadway, and a very small venue. Very intimate. The first few rows wear ponchos because stuff flies off the stage. Can't go wrong with boys

It's funny, interesting, amazing. They love, love, loved it. Totally worth the money.
Must do's for me would be Staten Island Ferry, Times Square, 9-11 area and Museum, New York slice of pizza, and Blue Man Group. Maybe the Empire State Building, but it's expensive, and my kids said it wasn't worth it. Everything else is gravy
