I’ve been to Air & Space several times but have never been out to see the stuff at Dulles. It’s on my agenda for my next trip to DC. The Boeing Museum of Flight is worth a visit if you make it to Seattle. There is some discussion of them getting one of the Shuttles when they are taken off line. That would be pretty neat!
Of course, going into/out of Alice Springs in a jump-seat of a Buff was a real treat!
I agree with the Boeing museum recommendation. Went there last year for the first time and loved it.
The Pima Air Museum in Tucson (next to the boneyard at Davis-Monthan) has an interesting collection of one-of-a-kind oddities. I also like the aeronautical museum in Balboa Park at San Diego.
The other landmark museum i’ve been to is at Duxford in England. They have excellent air shows in the summer months. The RAF museum at Hendon is also fantastic.
Still wanting to do Udvar-Hazy and Wright-Patterson.