This is a great comics shop with a wonderful variety of different comics. The staff is cool and friendly. They have every kind of manga and graphic novel that you could want. I believe they will even special order for you if what you are looking for is not in stock.
While you're here, check out Danile Clowes books such as Ghost World and his other graphic novels.
This store is in a strip mall on Rockvile Pike. It's on the top floor, so you have to climb one flight of stairs in the front.