Dulles Air and Space

Fantastic Museum, one of the newest ones. Parking was $12 dollars, however, I am sure you could park off the site and walk it in without anyone knowing.
Spent a good four hours in the museum looking and reading about aviation. Other cool items include Japanese, American and German experimental planes and guided rockets, along with, the Enola Gay and hte Concord (the Full B-29). The Enola is a HUGE airplane. Additionally, in the control tower they have displays and mockups of a modern aviation command and control.
The museum is still "in the works" some stuff is not out and the exhibits are not FULLY complete, but it is enough to get the gist. Another interesting item is a Vietnam era Huey and a collection of various early Balloon paraphenelia (like 1700s).
An interesting fact is the French at the seige of Paris during the Franco-Prussian War used balloons to lift supplies and people in and out.
Oh yeah, some other cool artifacts include coal from the Berlin Airlift, Eddie Rickenbacker's uniform(totally cool!), a SPAD and Neuiport WW1 aircraft.
I almost bought a book by John Morrow on WW1 Aircraft, but I have too many books already. :-)