Why is New York called the Big Apple?

Wikipedia covers this pretty well:

http://en.wikipedia.org/wiki/Big_Apple

Just an FYI. Minneapolis believe it or not is called the mini apple because of all the great theater!

Various accounts have traced the “Big Apple” expression to
Depression-Era sidewalk apple vendors, a Harlem night
club, and a popular 1930s dance known as the “Big Apple
http://www.salwen.com/apple.html

In the early 1920s, “apple” was used in reference to the many racing courses in and around New York City. Apple referred to the prizes being awarded for the races—as these were important races, the rewards were substantial.

Based on the research of Barry Popik, the use of “Big Apple” to refer to New York City became clearer. Popik found that a writer for the New York Morning Telegraph, John Fitzgerald, referred to New York City’s races “Around the Big Apple.” It is rumored that Fitzgerald got the term from jockeys and trainers in New Orleans who aspired to race on New York City tracks, referring to the “Big Apple.”

In the late 1920s and early 1930s, New York City’s jazz musicians began referring to New York City as the “Big Apple.” An old saying in show business was “There are many apples on the tree, but only one Big Apple.” New York City being the premier place to perform was referred to as the Big Apple.

http://gonyc.about.com/cs/atozinde1/a/bigapple.htm

The Big Apple. A series of citations, quotations, and evidence on the true origins of a New York City nickname, with additional material on other words and terms associated with the city. A web site by Barry Popik.
http://www.barrypopik.com/

Apple store buddy ;)