How about The Diner or Open City? When I lived in the neighborhood I ate at the Diner all the time or got take out. Their roast chicken is good as well as most of their sandwiches. And now they have mini burgers! :) Simple comfort food at a good price.
Sorry, you are right it is a big city. I'm looking for something that has components of meals, like a prepared food counter, but where you can stay and eat. Nothing cafeteria style.
The new Vapiano might be just the thing for you, then. It's actually a German chain, but just opened in the area. I haven't been to the one here, but people have said it's decent. There's one near Daily Grill in Dupont, and another is opening in Penn Quarter soon.