I just tried out Pizzeria Paradiso in Dupont Circle and they can make your pizza with soy cheese and wheat crust. I got the Margharita pizza and it was sooo delicious! They use the Follow Your Heart vegan mozzarella and it melts beautifully. I've also heard alot of good things about Sticky Fingers Bakery in Columbia Heights. I'm still looking for a good spot in Old Town, I've been using some vegan apps on my iTouch to find places.
The Big Belly Deli in Arlington makes some good vegan sandwiches (the reuben in particular) and the Sticky Fingers Bakery has the best cinnamon rolls I've ever had and these creme-filled oatmeal or devils food sandwich cookies that are pretty awesome. Yum.
I LOVE Sticky Fingers Bakery. I went there while on vacation in September. I had an awesome "tuna" melt with a side of tomato soup there. Yummy! Even went back before we flew home and got food to go on the plane.
If you are willing to travel to the suburbs, there are some good vegan restaurants such as Yuan Fu and The Vegetable Garden in Rockville, MD. A drive but it is fun is Great Sage in Clarksville, MD. It also has a natural food store next to it called Roots. MOM (My Organic Market) stores also carry The Vegetable Garden entrees in their refrigerated sections. The Vegetable Garden has 2 entrees on the menu that they say are macrobiotic. Yuan Fu is yummy but probably a little more heavy than The Vegetable Garden but they do have some entrees on the lighter side.
Also in DC itself (Adams Morgan), Asyllum is good for a weekend brunch indulgence. DC also has good ethiopian restaurants which you should try. They do tend to be a little greasy but I love ethiopian food and a veggie platter is vegan and is basically different types of spiced lentils, greens and often a small serving of salad and potatoes.
Oh and forgot to mention Soul Vegetarian, again in DC, walkable from Sticky Fingers. All their food is Vegan and it is soul type food. Some of it is not the best healthwise (Mac and Cheese!!) but it is a good indulgence.
Java Green in DC (I think they opened a location recently in dupont circle so they have 2 locations now) is a cafe with various korean inspired foods and they also have some raw foods. It is good, a little on the pricier side but I recommend trying it. They are not completely vegan so when they say cheese, they mean dairy cheese. They do have plenty of vegan options though.
I haven't been there but the Science Club in Dupont is vegetarian with some vegan options. It's more of a club/ bar with food served so good for going out at night. Here's the site: http://www.scienceclubdc.com/. I keep meaning to go there so if anyone has been let me know if it's good.
Java Green does have some regular chees options because they are not just a vegan restaurant - they are also serving vegetarians who still consume dairy, but they also offer soy cheese and the like. I read an article on them this summer that something like 50% of their customers are not vegetarian or vegan -- it's the flavors that keep them coming back. I love it!