Well IAD is hard to shoot at right now. Due to sun and construction and winds all combined. The observation deck is up and open now..but its not to great..sun is always in a bad position and not much taxis by but commuter stuff. The terminal windows once again in C and D are good..but only for watching. The sun during spring/summer goes more east and west..but in the winter its south all the time..making those spots great for pics. Outside when the winds are south, the best spot for 19L is at signature flight support parking lot..but since construction is going on, they're using an artificial threshold further up, making pic taking not really possible..unless somethin special comes in and parks in the signature lot. This spot is good for the 3PM-Sunset time. In the mornings though, theres a good spot in the postal parking lot. After on the acess road exit right where it says flight support, as if on your way to hawthorne. But keep back all the way through the construction, and turn up into the parking lot next to 1L/19R. or you can go to the north employee parking lot. in both spots keep a low profile. Not much comes in the morning, except ANA 744, and Saudi 744, and the Ethiopian 767. Right now thats the best spot, due to the construction on 19L.
Hope this helps a bit,
"..the joy of the Lord is your strength" Nehemiah 8:10