New York City's Economic Development Corporation drops a map that shows pizzeria density by ZIP code:

Using the latest available data from the Department of Health restaurant inspection results, we know this to be the East Village (zip 10003) with 33 pizza places. In Queens, Ridgewood (11385) has the most, while Williamsburg (11211) is number one in Brooklyn. Williamsbridge (10467) and Oakwood/New Dorp (10306) are top in the Bronx and Staten Island, respectively.

Neat bit of trivia from the EDC. Thanks!