I'm surprised that no one has mentioned the SAC Museum outside of Omaha. Three enormous warehouses with planes from WWII on including, from memory, among others:

SR71
U2
Gremlin (google that one)
Dolittle B25
B52
B36
British Vulcan
the list goes on and on.

BTW, my father flew 29 missions (yes, Catch 22) as a lead B24 bombardier during WWII in the Eighth Air Force. I grew up on the stories and a few years ago, found his flight logs online.