Jean Louis (Paladin) would have been my first choice but I think he has moved to Vegas of all places, used to be the best place in DC by a long stretch. Les Halles de Paris just around the corner from the treasury Dept on Penn Ave. It is a little pricey (but not as bad as the really fancy places) but if you like steak and provencal fare (rather than haute) then this is the place. Relaxed atmosphere and very good wine list. Have dessert on the terrace of the Hotel Washington next door.
If good Italian pizza and all you can eat spaghetti with a variety of different sauces piques your interest the IL Radicchio (one of Roberto Donna's places in DC, all of which are quite good) on 17th street near Dupont circle is your best bet. Though a line in the evenings is assured.
If Chinese is what you are looking for City lights of China is the best authentic style Chinese food restaurant in the city. It is on CT Ave a couple of blocks N of Dupont Circle. The embassy is just up the street and the staff often eat there. Couple of doors away there used to be a basement ice cream shop that did very tasty fare. Just down the street next to the circle is a place called afterwards Cafe (part of a bookstore) and has good coffee and desserts, is open very late and has outside seating which is great for people watching (Dupont circle is the place to go to see interesting looking people). Also everyone knows about all the big Galleries and museums along the Mall and elsewhere but a fine place that often gets overlooked is a place on 21st street called the Phillips Gallery (I used to live just up the street) which might be worth a visit in an effort to work up an appetite.
If you like beer then Brickskeller is the place for you, traditional bar fare as far as food goes but an amazing selection of beer and a fun atmosphere.
For the best chicken I have ever had there is a (Peruvian?) roast chicken take away in VA called Crisp and Juicy. Can't give you any more info than that but it was absolutely the best chicken.
Lebanese food at the Lebanese Taverna also on CT avenue on the right hand side after crossing the bridge from the Chinese embassy. Very good quality and reasonably priced. Few doors down in the basement is a place called Dolce finale, excellent dessert and tables outside.
There are just soo many good places all over DC (vegetarian place that serves Buddhist style cuisine that even a devout omnivore would love is called Vegetable Garden in Rock creek, Fortune at baileys crossroads for Dim Sum, etc).
I now have to stop as I am starting to envy you

Have a great time.
Address and phone number can be found at this web site for most of the places mentioned above.
http://www.district-of-columbia.com/diningout/