The longest in the U.S. is the Verrazano Narrows Bridge at 4260 feet (measured by length of main span or distance between towers). The Golden Gate Bridge has a main span of 4200 feet. The Verrazano Narrows Bridge lost the title of longest suspension bridge in the world in 1981 but remains the longest suspension bridge in the U.S.
I posted a riddle some time ago as to why the towers are further apart at the top than at the base. Anyone remember that?