Check out these links to read more about the real places:
Stylistic references of the AT&T Building on Galinsky.com
City Review article about changes made when the building became the Sony Building
Facts and a history of the bridge on NYCroads
David McCullough's classic account of the bridge construction: The Great Bridge, and the Ken Burns documentary based on the book: Brooklyn Bridge
The history of con men who sold the Brooklyn Bridge numerous times
New Yorker article about engineering flaws in the building secretly repaired in 1978: The Fifty-Nine-Story Crisis
Citicorp Center in The Midtown Book at the City Review
The Station at Citigroup Center, a fabulous miniature railway on display during the holidays
A description of Citigroup Center on greatgridlock.net
Great Buildings Online entry for Chrysler Building
Emily Zimmerman's essay Building the Chrysler Building
Another paper model of the Chrysler Building at Paper Toys.com
Higher: A Historic Race to the Sky and the Making of a City, by Neil Bascomb, published by Doubleday (2003)
The Chrysler Building: Creating a New York Icon Day by Day, by D. Stravitz, published by Princeton Architectural Press (2002)
Central Park 2000 description of Cleopatra's Needle
New York Parks historical marker for the obelisk
Nova Online's World of Obelisks
Walden Models features a free download of the matching Cleopatra's Needle obelisk now located in London
The New York Obelisk, by Martina D'Alton, published by Metropolitan Museum of Art (1993)
The official site of the Empire State Building
Emporis entry for Empire State Building
Great Buildings Online entry for Empire State Building
Lewis Hine photographs of the building construction: at Columbia and NY Public Library
NPR program about the history of the tower
Empire State Building: The Making of a Landmark, by John Tauranac, published by St. Martin's (1997)
Building the Empire State, by Carol Willis, published by W.W. Norton (2007)
Great Buildings Online entry for Flatiron Building
"The Flatiron Building at 100" on Flatironmag.com
Library of Congress film of a windy day at the Flatiron Building and the possible origin of the phrase "23 Skidoo"
The Flatiron, by Alice Alexiou, published by Thomas Dunne Books (2010)
General Grant National Memorial is run by the National Park Service
The Grant Monument Association has plans for its restoration
Groucho Marx popularized the riddle "Who's buried in Grant's Tomb?" on the quiz show "You Bet Your Life".
Information on the official Metropolitan Transit Authority website
Everything about rapid transit is on nycsubway.org
An animated map showing the growing web of subway lines
Casa Lever, a restaurant in the first floor of the building
The building is also the patron to rotating exhibits in the Lever House Art Collection
Skidmore, Owings & Merrill info about the project
Lever House in The Midtown Book at the City Review
Times Square Alliance tells the history of New Years Eve at the Square
Antique postcard views of One Times Square
James Lilek's history of Times Square buildings and advertising
Short description of the Seagram Building on Galinsky.com
The famous Four Seasons restaurant, located on the first floor of the building
Arch Daily Classics: the Seagram Building
The fascinating story of how the Mark Rothko murals commissioned for the Seagram Building ended up at London's Tate Modern museum
The Seagram Building: Building Blocks Series, photographs by Ezra Stoller, published by Princeton Architectural Press (1999)
Washington Square Arch in paintings and photographs on NY Architecture Images
The fight to 'Save the Square' from a proposed roadway in the 1950s
A history of Washington Square Park
Wikipedia entry about the social history of Washington Square
Paper model of the World Trade Center available from Fiddlers Green
A Japanese model of the WTC in 1:3000 scale from Paper Craft Maker
Joe Cangero's model of the WTC on cardmodelers.org
Andrew McCauley's model of the WTC
City in the Sky: The Rise and Fall of the World Trade Center, by James Glanz & Eric Lipton, published by Times Books (2003)
, and the Ken Burns documentary based on the book: 
, by Neil Bascomb, published by Doubleday (2003)
, by D. Stravitz, published by Princeton Architectural Press (2002)
, by Martina D'Alton, published by Metropolitan Museum of Art (1993)
, by John Tauranac, published by St. Martin's (1997)
, by Carol Willis, published by W.W. Norton (2007)
, by Alice Alexiou, published by Thomas Dunne Books (2010)
, photographs by Ezra Stoller, published by Princeton Architectural Press (1999)
, by James Glanz & Eric Lipton, published by Times Books (2003)