Thinking of kinda in the direction of Dulles (go somewhere and then IAD):

Leesburg has an old town -- shopping, restaurants, etc.
Manassas Battlefield, part of National Park Service
Marine Corps Museum, Triangle, VA
Middleburg, horsey-country
further out, Shenandoah National Park and various towns + nearby West Virginia, Fredericksburg, perhaps Gettysburg is too far
Woodlawn Plantation