The Steven F. Udvar-Hazy Center is part of the National Air and Space Museum and located in Dulles, VA just off Route 28 in Fairfax County. It can be found right next door to Dulles International Airport. It has an extensive collection of aircraft and a large exhibit of space elements including the space shuttle, Enterprise.
The museum is a great place to take the family. The kids can walk from plane to plane from the ground or stroll around the observation decks to check out the planes hanging from the ceiling. They offer several IMAX movies and simulators that get you right into the action. Once you have checked out all the planes you can take an elevator up to the Observation tower and see the planes taking off and landing at Dulles Airport. After 4:00 p.m. there is no $15 parking fee and great place for the kids to burn off some energy before dinnertime.