First, let me clarify the title. The Steven F. Udvar-Hazy Center is a museum annex of the National Air and Space museum. The Enola Gay is one of the airplanes kept there. The Enola Gay is the Boeing B-29 Superfortress that dropped the first atomic bomb on Hiroshima, Japan.
The Udvar-Hazy Museum is near the Washington Dulles International Airport in the Chantilly area of Fairfax County, Virginia
I took all of these pictures when I visited summer 2007.
Some of the exibits include:
the Space Shuttle Enterprise
the Gemini VII capsule
an SR-71 Blackbird
an Air France Concorde supersonic airliner
the Boeing 367-80 jet transport, which was the prototype for the Boeing 707
a Redstone rocket
the Langley Aerodrome A, an early attempt at powered flight by Smithsonian Secretary Samuel Pierpont Langley
the Northrop N-1
the only surviving Dornier Do 335 Pfeil [3]
the only surviving Boeing 307 Stratoliner, the ex-Pan Am "Clipper Flying Cloud"
the only surviving Heinkel He 219 Uhu
the only surviving Arado Ar 234 "Blitz"
one of three surviving Bachem Ba 349 Natters
the only surviving Nakajima J1N1 Gekko
one of four surviving Northrop P-61 Black Widows
one of two surviving Boeing P-26 Peashooters
a Bede BD-5, a single-seat, home-built aircraft that was somewhat popular in the 1970s
the Beck-Mahoney Sorceress, which is known as the "winningest" racing biplane in aviation history
a Hawker Hurricane fighter
a Japanese balloon bomb, such as the one that killed 6 US civilians in Oregon during World War II
Lockheed Martin X-35 Joint Strike Fighter, prototype of the F-35 Lightning II
F-14 Tomcat involved in the Gulf of Sidra incident (1989)
The Gossamer Albatross, which was the first man-powered aircraft to fly across the English Channel
The primary special-effects miniature of the "Mothership" used in the filming of Close Encounters of the Third Kind
The Virgin Atlantic GlobalFlyer, piloted by Steve Fossett for the first solo nonstop and nonrefueled circumnavigation of Earth