I'm not aware of too much in that part of the state.
There will be a new store in Charlottesville opening (I think) in November called Albemarle Aquariums and I like Aquatic Obsession in Manassas. A lot of people like Marine Scene in Herndon, but I think their prices are high.
I have bought some stuff from Winchester Pet & Aquarium, but you really have to look over what you're buying.