The Flatiron Building, was one of the tallest buildings in New York City upon its completion in 1902. It was designed by Daniel Burnham. The building took its name from the triangular lot it was built on (the Flatiron block, so called because it was shaped like a clothes iron). Today the Flatiron is a popular spot for tourist photographs, a National Historic Landmark since 1989 and a functioning office building, currently home to several book publishers. The surrounding area of Manhattan is named the Flatiron District for its signature building.

Sources, related links:
Wikipedia - Flatiron Building