I'm in Vienna, Va., and am darned happy to have Amma and Sunflower just down the street from me
I work in Reston. China Town's a fantastic place - it's in the Reston Town Center. It's a (healthy?) Chinese restaurant that does lots of great things with soy.
Also in Reston is the Tortilla Factory (fresh Tex Mex) - most vegeterian dishes can be made vegan by yanking the cheese (and sour cream, if there's any in the dish).
There's both an Indian and an Afghan (lunch) buffet in Reston (I'd have to look up the names - they're in the K-Mart plaza in Herndon) that feature about 50% vegetarian options, tho I wouldn't want to vouch for their veganness.
In Fairfax, too, there's ooo oo oo what's the name? Um. It's a fantastic all vegetarian Indian restaurant in just off Jermantown, 29, and 50. Oo! Woodlands! Great place. Bloaty.
Amma also has a location in Georgetown, fwiw.
In DC, Pizzeria Paradiso and 2 Amys (Dupont, G-town and... near Cathedral?) make fantastic pizzas - go cheeseless for the vegan in you.
And one of the tastiest bakeries I've ever visited (AND it's VEGAN!) is Sticky Fingers, just South of Adams Morgan (South of Florida) on 18th. OMG, try the cowvin cookies!
In Rockville (? Wherever White Flint Mall is, at any rate), don't miss the Vegetable Garden and its sister restaurant whose name I've completely forgotten.
OMG, I'm all hungry now.