Business travel takes me to the DC area a few times a year, and the Residence Inn Arlington Courthouse has become my hotel of choice. The location is very convenient to both the Court House Metro (about a block away) and Clarendon (6-8 blocks away). Between is about every sort of restaurant one could ask for at about any price range.
The hotel is always clean and well kept. The staff has always been friendly and helpful to me. I've only eaten the breakfast a couple of times (I'm usually on my way to the office or meetings by then), but it was decent. The rooms are clean and have everything I need when I stay in the area.
Because it sits on the Orange Line Metro, the location is very convenient to DC and National Airport.