Having spent a fair amount of time in DC for work and on
vacation, here is a couple of suggestions that I can offer.
It is a must to visit the memorials along The National Mall. Whether it is the
Washington, WWII, Vietnam War, Lincoln, or the Korean War Memorials, it is easy
for your spend several hours walking and exploring the area. My personal
favorites are the WWII and Lincoln Memorials. If you have the opportunity to
visit the Memorials at night, do so, they take on a completely different character
when they are lit up. Another must see is the US Capitol Building. If you happen
to be there on a weekday, PM me and I can try to get you on a private tour of
the Capitol. Otherwise on the weekend they have weekend tours available to the
general public. Arlington National Cemetery is pretty awe inspiring. I have
learned that the best time to visit Arlington is in the early morning when you can
be the only person other than the guards at the Tomb of the Unknown Soldiers.
For restaurants, I really like Brasserie Beck, which has a mind numbingly huge beer menu and good food to match the beers as well. If you like pizza, there is a good place called Pizza Paradiso located in Dupont Circle.
I hope this helps. Enjoy yourself in Washington DC.
-Jon