My favorite is Cafe X-Press (http://www.cafe-xpress.com) in Bethesda, MD.

All of their sandwiches are incredible, they are very affordable and the staff is very fast. Even when it is very crowded you can expect to be in and out of there in just a few minutes.

My favorite is the Manhattan, Hot pastrami & corned beef topped with cole slaw, melted Swiss cheese and Russian dressing on a sub roll. It is frickin awesome, and one of the things I miss the most about Bethesda.