Dominion is the local gold standard and is great. They do have a tour, and they are right near Dulles, good stop off for the frequent flier. Check out their Tuppers Hop Pocket, which you'll find in bars and bottles too, as well as their dominion ale, which is everywhere and great.

Dominion has a brewpub outpost at the convention center. And also, if you're transiting at Dulles there's a killer beer bar with a lot of good stuff on tap in the main terminal, just outside security (or it used to be, haven't been in a bit). I can't remember if it's a dominion place too or stocks various beers, I do remember spending a few hours there waiting for a delayed friend and thinking it was great.

Another local fave is Hook & Ladder. You see Foggy Bottom around to but I'm not a big fan.