I would definitely see the Holocaust Museum and the Museum of the American Indian. I'd also plan a little more time for my trip to the VA "branch" of the Air and Space, and allow a little less for the downtown visit; the downtown Air and Space is showing its age, and is not as remarkable or wonderful as it used to be. I agree with the poster who recommends stopping by the VA "branch" on your way in from Dulles; if you have a late flight in, stay out in that neighborhood and hit the museum in the morning. You have to take I-66 between IAD/VA Air and Space and the city and it's only 2 lanes inside the beltway; bumper to bumper more often than not and evening rush hour starts at about 2:30.

Since you will be here in the spring, I'd recommend the self-guided walking trails/tours as posted at http://www.culturaltourismdc.org/inf...nformation.htm. The Adams-Morgan trail would be my first pick, and U Street-Cardozo my second pick; both go through some of the more vibrant, ecclectic parts of our city, and you'll pass by many independant restaurants, cocktail lounges and bars so you can build an evening's entertainment from it. I would definitely NOT recommend going into Adams Morgan after about 9pm on a Friday or Saturday night as it is the major nightclub strip and the crowd is too annoying; close to impossible to walk down the sidewalk because of all the people.