You can't go up the Empire State Building and don't take a picture of the Flatiron Building. I think that, from above is how you can really appreciated this building, you haven't to choose a particular side, its strange form is enough to be the basis of a nice picture. Maybe the only "special" effect here is the light: I chose to go up the Empire at almost closing hour, when the sunset was starting and so I obtained that golden light you see.

 
by Elisa, Flatiron Building, New York City, 2000
http://www.elisarolle.com/travel/2000NewYork.htm

This picture was taken in 2000, my first time in NYC. This last September I did less tourist things, and so I didn't stay in line to go up again the Empire, but I did take another picture of the Flatiron, this time from below:

 
by Elisa, Flatiron Building, New York City, 2009
http://www.elisarolle.com/travel/2009EastCoastUSA.htm

The Flatiron Building, or Fuller Building as it was originally called, is located at 175 Fifth Avenue in the borough of Manhattan, and is considered to be one of the first skyscrapers ever built. Upon completion in 1902 it was one of the tallest buildings in New York City. The building sits on a triangular island block at 23rd Street, Fifth Avenue, and Broadway, anchoring the south (downtown) end of Madison Square.

The neighborhood around the building is called the Flatiron District after its signature building.

The Flatiron Building was designed by Chicago's Daniel Burnham in the Beaux-Arts style. Like a classical Greek column, its limestone and glazed terra-cotta façade is divided into a base, shaft and capital. Early sketches by Daniel Burnham show a design with an (unexecuted) clockface and a far more elaborate crown than in the actual building. Since it employed a steel skeleton, building to 22 stories was relatively simple and it was a technique familiar to the Fuller Company, a contracting firm with considerable expertise in building such tall structures. At the vertex, the triangular tower is only 6.5 feet (2 m) wide; viewed from above, this ‘pointy’ end of the structure describes an acute angle of about 25 degrees. The strong downdrafts in this area were reputed to raise women's skirts as they passed. New York's Flatiron Building was not the first building of its type: prominent examples include both the Gooderham Building of Toronto, built in 1892, and the 1897 English-American Building in Atlanta predate it, although the earlier buildings are smaller than their New York counterpart.

"I found myself agape, admiring a skyscraper — the prow of the Flatiron Building, to be particular, ploughing up through the traffic of Broadway and Fifth Avenue in the late-afternoon light." – H.G. Wells (1906)

The building, which took its name from the triangular lot on which it was built – the Flatiron block, so called because it was shaped like a clothing iron – was officially named the Fuller Building after George A. Fuller, founder of the company that financed its construction two years after his death. Locals took an immediate interest in the building, placing bets on how far the debris would spread when the wind knocked it down. This presumed susceptibility to damage also gave it the nickname Burnham's Folley. The building is also said to have helped coin the phrase "23 skidoo", from what cops would shout at men who tried to get glimpses of women's dresses being blown up by the winds swirling around the building due to the strong downdrafts. (from Wikipedia)