The Korean places in Annandale vary from everyday fast food, to sit-down expensive. If you are not familiar with Korean food, order Bulgogi or Kalbi (barbecued beef or ribs, respectively).
With your meal, you will get "panchan" which are small side dishes of all sorts of things from seaweed, fried or boiled potatoes, or pickled vegetables. You will also invariably get a portion of some form of kimchi -- either the standard cabbage variety or pickled cucumbers or "mu" (Korean radish).
When you go to a lot of the restaurants in here, you need to go with an open mind and be prepared to try things you have never eaten before. You might not like any of it, but you might find something you love.
*** It helps if you like spicy food!!!***
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Yechon
For standard Korean BBQ fare, try Yechon. This place is not at the center of Annandale, but is next to Little River Tpke & 495.
http://www.yelp.com/biz/yechon-annandale
This place is open 24 hours and can get very busy on the weekends, particularly between 10 p.m. and 1 a.m. on Friday & Saturday nights.
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To Sok Jip
http://www.yelp.com/biz/to-sok-jip-annandale
Really good "standard" Korean fare.
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Annandale Seafood Restaurant
If you are feeling a little more adventurous and are familiar with Korean food, my personal favorite place is called "Annandale Seafood Restaurant" but you would never know unless you can read the Korean/Hanja script above the door.
http://www.yelp.com/biz/annandale-seafood-restaurant-annandale
The seafood here is fantastic. You can get some of the best hand made sushi and sashimi here.
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With all of the Korean restaurants, the help is usually fresh off the boat Koreans whose English is horrible. The more authentic cuisine places' clientele is Korean, so they are not used to serving non-Koreans. You will get help ordering in most places, but don't expect to get your hand held.
Go and try this stuff. Most people will love Korean BBQ.