If you sit at a window on the left side of the plane you can see the Washington Monument, Capitol Building, Lincoln Memorial and White House (at least I think that was the White House). It always amazes me how close you are to these things when you land.
I saw all of that on my first trip into DCA. When I passed through again, I was mad because I was on the right side of the plane and couldn't see any of those things, then I finally took a glance out my own window though and saw the Pentagon up close and personal.
That's my favorite airport to fly into because you can see so many things.