Keste on Bleecker is by far the best pizza I've had in New York City -- south of 14th or otherwise. Motorino on the Lower East Side is also delicious.
http://kestepizzeria.com/ authentic Neapolitan
http://www.motorinopizza.com/

By the Slice try Joes on 6th & bleeker

Una Pizza Napoletana was indeed by far the best. I believe Motorino has taken over the shop so I'd give that a chance. I have to say I'm not a big fan of most New York style pizzas, including John's which I think is way overrated. A bit north of 14th, Pizza Fresca in the Flatiron area used to be top notch, but I haven't been there in awhile.

there is Lombardis downtown (i believe its on mott), or Rays on 11th Street and 6th Ave for a quick slice. Also, i'm a fan of patsy's on 10th street and university place.

I'm more of a Brooklyn girl, where I would recommend Frannies.

"Best" is quite relative :) We always liked John's of Bleecker at 278 Bleecker Street, between 6th and 7th Avenues. I'd direct you to Una Pizza Napoletana, which had probably the best pies in town, but Anthony Mangieri picked up and moved his shop to San Francisco.

You might get some answers when more members are around. But foodpickle is for cooks with last minute questions in the kitchen. Please feel free to use it when you have a kitchen emergency or are just stumped.