In DC for 3 days, what are the can't misses?...
For a unique joint kind of place, try Ben's Chili Bowl and get a chili half smoke, fries and a shake. A great lunch.
Two Amys Pizza a bit away from downtown (to say the least) is worth the trip as the pizza is very good, but they do not take reservations and it gets kind of crowded and noisy. But the food is good.
Jaleo and Zaytinya are worth it for tapas or mezzes, and you can graze. I think the food is better at Jaleo. Zaytinya is where all of the beautiful people go to be seen, IMO.
To splurge, get thee to Palena, in the back room.