Yechon is an Annandale institution. It is a consistent, reliable standby that serves a wide variety of Korean staples 24 hours a day, seven days a week. Most non-Koreans probably come for the BBQ (which I have yet to order), but there are plenty of items to choose from on the menu for bold epicurean or even the slightly less adventurous palate.
For those seeking to expand beyond Korean BBQ, try the dolsot bibimbop. It essentially is rice served in a hot, stone bowl with various vegetables, both pickled and fresh, tossed in with a portion of Korean BBQ beef (bulgogi). When mixed together with the hot pepper paste and a little sesame oil, you get a nice melange of earthy spiciness, piquant acidity from the vinegary vegetables, and the heartiness of toasted rice. I would also urge you spend the extra money on the hot, stone bowl: the slight crust it develops on the rice really elevates the dish. They also have bokumbap, which is a Korean fried rice dish, that is a little softer and less sauced than Chinese fried rice. The stir-fried noodle dish (japchae) is also well made and an utterly correct rendition.
For the more adventurous, I am a big fan of their oxtail soup (kkori gomtang) which is essentially just a milky beef broth made by slowly boiling beef bones and oxtails for several hours. It is a very refreshing dish, though many would probably characterize it as bland. But, throw in some diced scallions, salt, and red pepper, and it becomes a marvel of simplicity. On the other end of the spectrum you have the spicy buckwheat noodle dish (bibimnaengmyung) which is served cold. Traditionally a summer dish, I think it is still suitable for the fall.
The gratis banchan dishes are all solid if unspectacular. The radish kimchi (kaktugi) is good, though I find the cabbage kimchi (baechu kimchi) a little bland. The potato salad and bean sprouts are nice.
All in all, I ate with two other people and we got a huge spread for $40 plus tip. Service is efficient and polite and the ambiance is quiet and sedate (though I hear that it is quite hopping late night on weekends). It is a good place to go to try Korean food for the first and you really can't go too wrong with any of the Korean dishes they have to offer: probably one of the more consistent menus I have tried in Annandale.
N.B.: One amusing detail my sister noticed as we left: the staff were eating Domino Pasta Bread Bowls for dinner. I guess even they get tired of Korean food (though I suppose it shows that we generally can't really kick our love for carbs).