I took that on a Sunday morning in June or July. It's amazing how quiet the town is at that hour. Whenever I want to get pictures in the city, I hit it on Sunday morning. We got some shots in front of the Capitol and Washington Monument as well.
There's a little bus stop area Southeast of the Lincoln Memorial where you may be able to get a good shot with the Monument and/or reflecting pool/mall in the background.
The Northwest side of the Capitol has a lot where you can park and get some good shots as well.