I'm so jealous!!! DC is one of my favorite places to visit! If you are looking for the top museums, I've got to say the American History and the Air and Space Museum. American history has pieces from pop culture (Mr Rogers sweater, Oscar the Grouch, Ruby Slippers), ballgowns worn by the First Ladies, and a bunch more really awesome stuff. They also just redid it recently (during my last 2008 trip) so it will be brand new! The Air and Space museum has planes, space crafts, and a bunch of interactive stuff...super cool.
Those are my top two, but other suggestions:
-National History Museum...see the Hope Diamond (and other jewels)
-Archives...see original Declaration, Constitution and Bill of Rights
-Go up in the Washington Monument (awesome view!)
-Union Station Metro Stop (really pretty building, shopping, and awesome food court)
-RIDE THE METRO AT LEAST ONCE!!!! (honestly one of my fav parts of DC)
And just enjoy it all. The way my family does it, it's a ton of walking and super exhausting but it's worth every minute of it. Have an AWESOME trip!!!
