Another of the largest was just a temporary guest: the great garrison flag that hung from the façade of the Pentagon from September 12 to October 11, 2001. Fittingly, the installation was in Flag Hall, where the Star Spangled Banner was formerly displayed.
I was lucky enough to see it when it was on display from 2002 to 2006.
It was a striking sight whose power the photo can barely convey, though the visitor's head and top of the Christmas tree at lower right give you some sense of the scale.
It is now back home in storage at the U.S. Army Center of Military History at Fort McNair.
National Museum of American History online exhibit, September 11: Bearing Witness to History.