I don't blame you at all! When I lived in D.C I would often eat at the cafeteria on my school campus, but on those times I would go and eat off campus I'd go to little hole-in-the-wall places right off the metro stop.
My favorite place to eat while living in D.C was a sub shop called 'La Bamba' (not the restaurant in Silver Spring, MD). It's on Georgia Ave right across the street from Howard Universities 'School of Business'. There was also another hole in the wall place on the corner of Georgia Ave. and Gresham PL (just down the street from La Bamba's...sadly I can't remember the name of it) that has the best chicken strips and sweet and sour sauce ever yum! Just a heads up, don't be freaked out if you go and the storefront looks really ghetto...the food is yummy and I remember the service being really good and the prices reasonable.
5 Guys is a must! It's the only burger joint I've ever been to where you can scoop a pail of peanuts and eat them while you wait for your food! Another good place to eat is Ben's Chili Bowl. Its right off of Georgia Ave and U street. They have good chili dogs and I used to always order a slice of cake to go! The restaurant is pretty famous too! I've heard it was in a few movies and celebs have visited the restaurant all the time. Who knows, maybe you'll walk in and meet someone famous!
There's also a bunch of little places on 7th Street right in China Town. I remember a mexican food restaurant I think it was either La Tarasca's or California Tortilla. They were pretty reasonable and the food wasn't too bad. There's also more mainstream places in China Town like Fuddruckers, Ruby Tuesday's, and Chipotle.
I haven't really tried a lot of food in Georgetown. The only places where I ate in Georgetown were at Uno's Pizzeria and then a seafood restaurant that I believe is called "Manhattan's" (Both on M St.) But from what I remembered...Manhattan's was a little more on the pricier side.
Adam's Morgan is another cool place to check out if you're looking for ethnic food. Sadly, the only thing I ever had there was Maggie Moo's Ice Cream (kind of like Cold Stones). I wish I was able to go there more frequently and try new things.
Another place you could check out is Crystal City in Alexandria. I remember eating these really yummy quesadilla's at 'Don Pablo's. Unless you take a bus or car, it's kind of a far walk from the metro.
Someone who commented here also mentioned something about going to an Olive Garden. I totally agree with him! While I do believe you can find something reasonable within the city, if you want something like Italian food, I'd check out an Olive Garden or maybe a Macaroni Grill (there's one in Silver Spring, MD). The quality of food is probably just as good, or if not better than some of the other 'non-mainstream named restaurants' in the city, and you'll probably pay a lot less.
Anyways enjoy your trip, make sure to pack some warm clothes and don't forget to check out some sites too!