Taqueria El Charrito Caminante is easily the best taqueria in the region. In first place are the goat tacos, but they also have fine chorizo and pretty good pork. They also make burritos, but I've never had them.
Venerable Chowhound John B always got the chorizo burrito.
El Charrito Caminante
2710 Washington Blvd, Arlington, VA 22201