This is by far the best campground I've found within a few hours of DC.  I've posted some pix, take a look.

Small, quiet, directly on two streams, one of which is trout-stocked.  I stayed on a Tues-Wed evening during the summer, and was the only person there both nights.  My campsite was the best one, right in the corner where two streams join together.  

The streams were awesome...fast-flowing, ranging from ankle to knee deep.  There are trails from the campground along the streams, with several crossings.

Campground is small--only nine sites total, seven of which are on the streams, two in the interior (about 40 yards from the streams).  Clean cinder-block toilet.  Bear-proof trash cans.  First-come, first-serve, no reservations.

A couple of caveats about this place: 

1. it is small, and according to the manager it is full pretty much every weekend during the summer, so don't count on getting a spot there--plan to arrive early and have a Plan B in case it is full.

2)  For some reason alcoholic beverages are not allowed in this campground.  Not sure how strictly it is enforced, but if you want to bring some beers you should probably be discrete about it.