http://dc.about.com/od/restaurants/tp/gourmetfoods.htm

Gourmet International Market: http://www.rodmans.com/ 5100 Wisconsin Avenue Northwest, Washington D.C., DC 20016-4123

Excellent wine and spirits: Schneider's of Capitol Hill http://www.cellar.com/

Amazing hard-to-find liquors: Ace Bev

P and C Market carries gourmet items and Polyface meats: http://www.facebook.com/pages/Washington-DC/PC-Market/164589065004

Arganica - http://arganica.com/ brings fine farm products to your door

Fine wines, liquor and cheese: La Cheeserie http://www.dcfoodies.com/2008/02/la-cheeserie-at.html 4339 Connecticut Avenue, NW (one block from Van Ness/UDC Metro stop)

More cheese and wine for the Virginia crowd: http://www.cheesetique.com/

This Virginia store rents raclette equipment: http://www.theswissbakeryonline.com/

3 Stars brewing and supply in Takoma: http://3starsbrewing.com/

A nice roundup of "foodie" stores in the DC area: http://www.washingtonian.com/articles/food-dining/where-foodies-shop/

Ethnic Food Stores

All things Latin at the Mega SuperMarket near Takoma Park (at University and Piney Branch)

Latin grocery store recommended by Pati! http://www.yelp.com/biz/panamericana-grocery-washington

Capital City (Florida) Market: http://capitalcitymarket.blogspot.com/ has tons of stores (map on that page) with hard to find african, indian, and latin american items, and of course A. Litteri's : http://www.litteris.com/

Caribbean Market II http://local.yahoo.com/info-12487321-caribbean-market-ii-takoma-park

Japanese: Hana Japanese Market, 17th & U

Grand Mart - Wide (and reasonably deep) selection of asian, hispanic, and middle eastern items. Seriously every other ethnic market combined. Multiple locations:
6255 Little River Turnpike, Alexandria, VA 22312 - Right off 395 @ Little River Turnpike)
6326 Arlington Blvd, Falls Church, VA 22042 - Seven Corners

H Mart - Nice selection of asian items with a focus on Korean. Multiple locations:
8103 Lee Hwy, Falls Church, VA 22042 - Across from Merrifield Garden Center where 66 and 495 meet
10780 Fairfax Blvd, Fairfax, VA 22030 - Supposed to be biggest and best
7885 Heritage Dr, Annandale, VA 22003

Levantine treats: http://sauson.com/

Mediterranean Bakery & Cafe : https://www.yelp.com/biz/mediterranean-bakery-and-cafe-alexandria Pita baked on site

Persian and -Stan foods, plus Ethiopian injera: http://www.yelp.com/biz/fair-price-international-supermarket-alexandria#...
Indian/Pakistani foods: House of Spices (Forestville, MD) http://www.hosindia.com/

A good roundup of a variety of international markets in DC and the burbs: http://dcist.com/2014/05/the_nine_best_international_food_mark.php
And another: http://www.northernvirginiamag.com/noodles-buying-guide/

Online Stores

Murray's Cheese - recommended by the cheese guy (and his cow-cart) at the Inn at Little Washington (I liked the swiss cow's cheese, Vacherin Mont d'Or)

Shallon Wine in Astoria, Oregon, which makes a chocolate wine.