If you've got kids, I highly recommend the New York Hall of Science in Queens. They've got this massive Science Playground and interactive exhibits for a whole range of tykesters.
Went there with the girlfriend and child yesterday and there was sooo much more to do and see than we expected. (Made this video featuring one ball-track exhibit in the playground: there is really an embarrassing amount of stuff for kids to do in that playground.)
New York Hall of Science: Malice Highload's Kid Pick of the Week!