That said, you might have a go with this list instead: http://www.vegdc.com/restaurants.php.
Some of my favorites from my time in DC:
Busboys and Poets: not all vegetarian, but vegan options each day and all sort of live entertainment.
Java Green: sandwiches, soups, pasta, etc...very yummy (though I'm not a fan of the baked goods)
Nirvana: yummy Indian fare
Soul Veg/Everlasting life: good prices, good food, good company (you have to have the carrot salad!)
The Black Cat: club/music joint with lot of vegan options
there's this really yum place in Eastern Market too, but for the life of me, I can't remember the name. My sis lives there though, so I can ask her.
Also, you absolutely must include a visit to Sticky Fingers Bakery. It's all vegan and to die for.
I can also recommend Hard Times Cafe - there are several locations around town. In this cold weather we've been having, their vegan chili hits the spot perfectly.
I suggest Galaxy Hut in Arlington; it's along Wilson Blvd. in the Clarendon neighborhood. A very vegan friendly menu, good beer choices, and a nice hipster-ish dive bar vibe (Well, the best you can do in Clarendon).
Another great place is Sunrise Caribbean in Union Station; if you work nearby or take the red line anywhere it is worth the stop. They've amazing greens, at least 3 types of vegan meats every day, and the best vegan mac in the city. Sensible prices as well.