New York City is an unusual one to lump in there, it's definitely the oddball of that set. There are two specific neighborhoods that are the most interesting at night in Manhattan (Williamsburg would be on the list if we were talking about Brooklyn).
-Meatpacking. Really a very small neighborhood, but as dense as Lan Kwai Fong. The Boom Boom Room at The Standard is worth a stop (beautiful gals, great views), there's Cielo, Le Bain, Gaslight Lounge, and Bijoux. These places are all within a stone's throw from each other.
-Lower East Side. Incredible scene and very diverse. Schiller's, Fig 19, Apotheke, Whiskey Ward, Marshall Stack, many many places down here for having fun. This is a much later scene -- some of these bars are basically empty until midnight, and don't get really going until 2am...
Of course you ask 10 different people you will get 10 different lists. But the above places are all PUA paradise!!!