For Korean food try Lotte in Silver Spring, Maryland. It's decent for the basics and they have a Chinese foods aisle. But an even better reason to go is that on the weekends they make fresh hottok outside in the back parking lot! Oh and sometimes they make that fish thingy with sweet bean paste filling. Hottok is sooo good this time of the year.
Lotte 13625-A Georgia Ave., Silver Spring, MD 20906
In addition to those mentioned already:
Rockville has its own Lotte (Korean) and a Kam Sam (Chinese). In Virginia, Merrifield has Great Wall (Chinese) and an H-Mart (Korean), while Annandale has a smaller Kam Sam.
There are Grand Marts (Korean) throughout the Metro area, but they vary greatly by location in terms of ingredients selection and cleanliness. The one in Sterling, VA by me is very clean and has a wide selection of Asian and Hispanic ingredients.
In my opinion, the Super H in Fairfax is much better than its Korean competition: the Lotte in Fairfax and the Grand Mart in Falls Church. In addition, the price and quality of the produce at Super H is much better than at any other supermarket in Northern Virginia, ethnic or otherwise.