L&B Spumoni Gardens is pretty good (it's all about the sauce IMO). It's not nearly as greasy as Chicago style pizza, but quite different from the typical NY-style Neapolitan pie and way better than most of the rock-hard reheated Sicilian slices you'll find at many slice joints around NYC. I'm not sure it justifies a schlep out to Bensonhurst the way DiFara's justifies the trip to Flatbush, but if you find yourself out there already, definitely stop in and try it.
Everyone else is right that Chicago-style pizza is (1) an abomination and (2) not something you should even consider eating while in NY. That said, if you really, really want to try it, and can't actually get to Chicago, Uno Chicago Grill does have a couple of NYC franchises (as mentioned upthread). And Uno is a corporate chain descended from the original Pizzeria Uno in Chicago, where deep dish pizza allegedly originated.