I'm responding to a post I saw on the old list re DC restaurants. As a former DC resident I have a bunch of suggestions. I'm assuming you are going to be in DC proper and have suggested accordingly.
Best eating experience in the city (to my mind) is minibar at CafeAtlantico. It is called minibar because it is a seemingly endless parade of "mini" absolutely delicious and cutting edge food science stuff. Some of my favorites were the "deconstructed" glass of white wine, foie gras wrapped in cotton candy, kobe beef with a truffle scented napkin, canteloupe balls - made right in front of us using some sort of chemical to lightly solidify the outside of liquid sponfuls of canteloupe soup. Minibar will run you well over $100, but if you go with a friend it will be a fun experience that lasts for a couple of hours. They have two seatings at the six person bar, and they make all the dishes right in front of you so you get a show with your dinner. If you can't get into minibar the regular CafeAtlantico restuarant is also excellent.
Teaism - delicious breakfast and lunches and an array of teas. In Dupont Circle and Penn Quarter, a nice change from that Starbucks coffee and scone.
Indique - Fantastic Indian food in the Cleveland Park neighborhood (on the red line). In between moderate and expensive.
Palena - Also in Cleveland Park. Fantastic food at a very reasonable price if you eat off the "bar" menu. I occassionally dream about their cheeseburgers (apparently the secret is truffle oil in the cheese) and they have an out of this world roast chicken. If yo go don't miss the "fry" plate which includes fried lemon rinds, twice baked potatoes and other delectable goodies.
Thai. There are a ton of great thai places. In Dupont Circle - ThaiChef is slightly better than Thaiphoon, but they are both excellent. ThaiChef also has excellent sushi. In Penn Quarter/Chinatown Kimalaya is very good - not great. Dungrats, which is in Northern VA, is the best in the whole area.
Let me know if you are looking for any specific suggestions in terms of neighborhoods or food types and I'll make some suggestions. Also, check out washingtonpost.com for good reviews and help in finding a restaurant.
