Right next door to Mixtec is another excellent and inexpensive choice that stays busy all night. You might have to wait for a table, too, especially on a Friday or Saturday night, since the restaurant doesn't take reservations. But you'll agree that it's worth it, after you dive into a plate heaped with one of the nearly 25 pasta dishes on the menu. Eight have meat sauces, three have seafood, and the remainder are vegetarian. I recommend the green fettuccine with creamy porcini-mushroom sauce. Bread is made in-house, and appetizers, like the Caesar salad or fresh mozzarella and tomatoes, are all flavorful. This place is as low-key as Washington gets, with a simple, brightly lit interior of red-checked covered tables packed together, and dishes served to a table as they are ready.