Blanca's
Blanca's, 418 S. Washington Street, Falls Church, VA, Rt. 29, 703-538-2466 (Metro Trip Planner - opens in new window) [Falls Church News-Press | City Paper | Yelp]
Actually an El Salvadorean restaurant, but they also have excellent Mexican food, the best in the area outside of the old Cielito Lindo in Bladensburg. Get the bean burrito. Don't go when you are in a hurry, however. Any of the non-Mexican Latin places that try to make quasi-Mexican food will beat the pathetic American attempts at Mexican food found in this area.