The store finder up top has locations and some info.
http://www.dakkadakka.com/core/store_finder.jsp
The big question is do you have a car? None of the stores in the
DC area are easy to get to by Metro.
For supplies and models I recommend Hobby Works, it's primarily a model shop with some
40k stuff and they have tons of models I've not seen anywhere else. Good for things like Pegasus Terrain, plasticard, and sci-fi models.
But it's 45 minutes drive from
DC.
Compleat Strategist and Victory Comics are both fairly close to East Falls Church Metro and have some unexpected stuff. They're about a 15 minute walk from each other too.
CS is a pure gaming shop,
VC is a mixed comic/toy/gaming shop.
Hope this helps.