Hi! I've lived in the DC area for a year and a half now, and there are some great new breweries here.
In DC proper, I recommend Bluejacket at The Arsenal (good variety with a growing sour program), Atlas Brew Works, Three Stars and DC Brau - all make good quality beer. I also recommend Port City Brewing across the river from DC in Alexandria, Virginia.
In the Shenandoah area, Star Hill in Crozet, Virginia has excellent beer. Devil's Backbone Brewery and Lickinghole Creek Farm Brewery are also good (though Lickinghole Creek is a bit of a drive from Shenandoah). I have also heard good things about Wild Wolf Brewing and Blue Mountain Brewery.
Enjoy your visit! Shenandoah is one of my favorite National Parks, and the fall colors in October should be gorgeous.