#1- Smithsonian: Air and Space. It isnt a real DC visit until you have been there.
#2- If you dont mind jumping through about 20 differnt security points, you can go and see the Capital. I got in through Brownbacks officers there. You can sit on a seat overlooking the senate floor, and they have some museum stuff you can go to. Worth going through the security IMO.
#3- Holocaust Museum. One of the only times I was actually slow and quiet going through a museum. Seriously, there are some things you cant unsee, unread, or unhear. All of my years of researching it (8 years total) had never prepared me for that.
#4- White House.
#5- Various memorials. Vietnam, WW2, Washington, Jefferson, Lincoln.
#6- Arlington National Cemetary. If you go there, make sure you get there at the top of the hour. The changing of the guards at the tomb of the unknown soldier is a sight to behold.
#7- US Navy Muesum. Located at the Navy yard. It is kind of small, but still very good. They also have a decommissioned Cold War destroyer there that they allow people to go out on, as well as the biggest artillery yet devoloped by the US, the 15"/50 caliber Railway gun used in WW1.
As for some interesting things I saw when I was there (but wont happen again because they were just luck.)
#1- When we were going to the Kansas office to head to the Capital, we got stopped by some people in black uniforms. Then, 3 black SUVs pull up. More people in black get out of the front and back one, then got to the middle one, and wisked someone inside. My dad, who keeps up on politics and leaders, was the only one to get a really good look at him. Who was it? Leon Panetta, director of the CIA. [http://en.wikipedia.org/wiki/Leon_Panetta]
#2- When we were passing the FBI building, we saw a car leaving with heavy escort. While the guard couldnt tell us who it was[footnote]My dad got this little exchange with him: D) Who was that? G)If I told you, I would have to kill you. D)Well, just tell me and then you can shoot me, make something up. G) Nah, theres too much paperwork for that.[/footnote], we think it was the director of the FBI.
#3- When we were just walking around, we had the Vice Presidents motorcade pass us. My dad knew it was the VP because there was no ambulance with the convoy, and the president always has one on hand.
Captcha- sound of sirens
Happened alot when I was there.