Can you provide a little more detail on what you're looking for? I'm vegetarian and lived in DC for a while so have a pretty decent sense of the scene-- Indian restaurants are obvious, and can make some other basic suggestions:

For example, for Thai food, Duangrat/Rabieng at Bailey's Crossroads in VA have wonderful veg. selections on the menu-Ethiopian is another good bet-- try Meskerem on 18th St. in Adams-Morgan or Zed in West End/Georgetown. Middle Eastern--Lebanese Taverna or its upscale cousin, Zaytinya.

Are you looking for fine dining places? Restaurant Eve in Alexandra will do a spectacular veg. tasting menu with advance notice. Nora on Florida Avenue in Dupont always has a vegetarian tasting menu available and its been excellent the few times I've been.

Again, give me more specifics and I can provide more ideas.