NYSE
The New York Stock Exchange, also known as the "Big Board," is the largest equity exchange in the world based on the total market capitalization of its listed securities. Formerly a private company, it went public in 2006 and at the same time acquired electronic trading exchange Archipelago. The parent company of the New York Stock Exchange is now called NYSE Euronext, following a merger with the Euronext group of European exchanges in 2007.
See also: http://www.nyse.com/.