Samir L: Forget all the other Smithsonians, this one is the bomb. *Hangars* full of awesome aerospace history, including a retired space shuttle! (Also: largest IMAX screen in Virginia was great for Star Wars)
Samir L: Reserve tickets in advance online (sometimes months in advance) or show up first thing in the AM for day-of tickets. https://www.nps.gov/wamo/planyourvisit/fees.htm
Samir L: Spot the Darth Vader gargoyle, and go here during the fall/winter (when the trees have shed their leaves) for an awesome vantage point of DC (see also: L'Enfant's Grave)