As a native MD/DC/NoVa resident/diner, I feel the need to throw my two cents in to a couple of thoughts made already in this thread.
First off, I live in Gaithersburg... and really don't like Giuseppis (sp) pizza; it's just too greasy for me. That said, I can see how it might get praise considering the admitted lack of good pizzerias in the DC area. Potomac Pizza (another place in the same neighborhood as Giuseppis) also makes a pie I'm not a fan of, but their subs usually don't let me down. I'd rather go to the Italian Market off Quince Orchard rd. anyday, as it's about as close as you can get to "real" Italian food/pizza. One last Gaithersburg note: I've never been to Joe's Pizza and Pasta, but I have actually heard good things from more than a few sources. Don't know why I haven't tasted it out yet, but I'd still recommend giving it a shot.
Moving from that, I recently tried Vapiano's, a pizza/pasta place in Ballston, VA on Wilson Blvd. It was interesting, to say the absolute least: different stations are set up, each serving one category of food (pizza station, pasta station(s), dessert station, bar station). Without ranting too much about the place itself, the pizza wasn't the worst I've ever had (and this coming from a Maryland boy). I got the Pizza Crudo, which is basically a pie with mozzerella and procuitto di parma. Everything is made in front of you, so the freshness of the ingredients was never in doubt, and the wait is not long at all. I usually prefer a deep-dish, Chicago-style crust, but the thin crust they use isn't overloaded with grease, and it certainly doesn't have any "tip sag" to it. It might not be everyone's cup of tea/beer, but I'd say Vapiano is worth a sample.
One other DC-based place I *might* recommend is Matchbox, located in Chinatown. Again, I haven't had the pizza there, but it definitely looked considerable. Off topic: the mini-burgers there are FREAKIN AMAZING.... but I'll refrain from going on about those. Two Amys is also supposed to be written up as great, but I've never been there and I have no intention of trying them anytime soon - I've heard my fair share of bad experiences.
Hope some of that helped. Remember, MD/DC/NoVa isn't a *complete* culinary wasteland... worst comes to worst, we can still do crab pretty damn good.