Watergate
From dKosopedia
Scandal that brought down Richard Nixon. Broken by Bob Woodward and Carl Bernstein in the Washington Post. Named after "The Watergate Hotel", a building in DC which at the time housed the Democratic Party headquarters.
The Washington Post has archived much of its Watergate coverage on the web, here.
The Watergate scandal is the source for the annoying naming convention used in many political scandals. For example, Travelgate and Nannygate.