On a recent Southwest Airlines flight departing from Reagan National Airport at sunset, I had my preferred aisle seat (12A) and was able to capture a few images with what I considered to be interesting views. I had access to the Washington Monument and the US Capital as we were taxiing to the runway followed by Crystal City (Arlington County) as we took off, and then the Pentagon with the Air Force Memorial in the background as we were airborne.
Personally, I always enjoy seeing Washington DC and the Pentagon from an airplane when I leave Reagan national Airport.