Tell us more about where (generally) you're staying, what kind of time you have, and what you like doing. You'll have the run of the city, lots of people get out of town that weekend.
We've got lots of ideas for you, just help us narrow it down!
Night of 4 of July - get to the East River to watch the fireworks. There are some bleacher areas, and lots of riverside parks, and of course the South Street Seaport is a good spot, but hopefully someone can link or Google the fireworks. I think Macy's sponsors it.