I know you can get prints from camera stores like Ace Photo in Ashburn, Dominion Camera in Falls Church and Calumet in Tysons. I haven't used them for digital prints just developing, scanning and film prints.
I'ved used Costco, Snapfish and Mpix online for whats its worth
I live just south of the DC area (Fredericksburg area) and I and a lot of other serious photographers use the local Costco. They keep their printers well maintained and calibrated. Profiles for them are available at Dry Creek Photo.