I didn't read through the whole thread because I'm lazy but my all time favorite is Scales. It is the BEST fish store in the world. Friendly staff, everything is very clean, prices are pretty good, staff is knowlegable, very nice selection (not just your ordinary stuff) and they even quarantine the fish before they sell them. They have fresh, brackish and marine.
They're in Silver Spring. Montgomery County maybe?
744 Cloverly Street, Cloverly, MD 20905
Aquarium Store, Freshwater, Saltwater-SCALES Tropical Fish Warehouse
I'm not affiliated with them but I love a good lfs
when I see one!