depending on what time you wanna get it, "Checkers Diner" right by AuP/Whiteys/G&C has good breakfast, but they close at like 3 in the afternoon, and serve only breakfast/lunch. Expo Cafe behind the Dulles Expo Center is good, and cheap, but both of these are little diners, not a sitdown nice restaurant kinda place
checkers just has good food over all
also x2 for yorkshire