Go up to Baltimore (Timonium actually) to Gramophone. They have multiple HT rooms for each price point up the line. And I mean HT rooms. They are set up with sofas, etc just like you would have in your house. They have regular listening rooms also. Their web site is http://www.gramophone.com/
Also in Baltimore is Soundscape. A small place, but the staff is friendly and know their stuff. Web site is: http://www.soundscapeaudiovideo.com/
Soundworks in Kensington is one of the best places near DC (if not the best). They are worth the trip. They have a lot of listening rooms at all price points.
Myer-Emco is DC's B&W dealer if that is what you're looking for. (Gramophone and Soundscape are also). http://www.myer-emco.com/