Some great alternatives to DC area are Hill Aerospace Museum at Hill AFB in Ogden, UT, and the National Museum of the Air Force at Wright-Patterson AFB in Dayton, OH. Hill has an amazing collection of ICBMs and nearly every other type of AC you can think of along with its own crown jewel SR-71 Blackbird, and Wright-Patt is even better. I'm sure there's a few others out there, those are the two that I personally know of though. The may not have an Enola Gay, toasted Mercury capsule or the Glamorous Glennis, but the aircraft they have are diverse and still tell amazing stories.
Like most, the things that go real fast or came from other Skunk Works projects draw my attention the most, but what really gets my brain going is looking at an old P-47, P-51, F6F, or F4U and think of the men who flew them in WWII, the old school seat of the pants flying skill they possessed, and the many that went down in them for the sake of the men on the ground and those flying off their wing. I have nothing but the utmost respect for those fallen angel aviators and those who went on to either "regular" lives flying for TWA or the Chuck Yeager types who pushed the limits to help us achieve our seemingly perpetual superiority in the air and beyond. I've been fortunate enough to have met a few of those guys, very cool cats for sure.