Aquilla, I recommend the new WWII memorial on the mall, it's quite well done. If you like ethnic food at all, head up to Addams-Morgan, there's a lot of good eats up there. More than a few excellent ethiopian places like Addis Ababa. If memory serves me, go up 18th till you get to the blocks past U sreet.
The National Zoo is fun, and free. Of course the Smithsonian. I like the Hirschorn myself, but they're all good. If you like live music, make sure and grab a copy of the City Paper (free), and check out the scene. The new 9:30 club is one of the best venues on the East Coast.
Arlington Cemetary is a beautiful and sobering place to visit. Oh, and if you see any notices about the Army Band playing in town, check it out - my sister (that's Sgt. sister to you) is in the viola section!
If you go west on Constitution, and go across the river, there's some good restaurants over there, too.
Don't listen to what people say - DC is an awesome place. I love just walking around checking out the architecture.
And hey - see if you can get a picture of a Free Speech ZoneŽ for me!