Exotic Aquatics: This is a nice shop. They have a nice selection of corals and inverts. Prices are average on livestock, a bit pricey on dry goods. Overall I like this shop.
Aquarium Center: Large selection of dry goods and decent prices. Good selection of fish at average prices. Coral selection is OK, prices the same. Inverts decent, but prices higher on small stuff (snails, crab, etc). Worth the trip.
House of Tropicals: Last time I was there they had a nice selection of corals. Not much in the way of fish (reef wise). Prices on the high side.
Not too far from Baltimore:
The Reef Tank: This is one of my favorite shops. It is located in Northern Virginia. GREAT prices on everything they carry. Don't stock a lot in the way of dry goods, but will order anything.
Marine Scene: Also in Northern Virginia, not far from The Reef Tank. Worth a visit if your in the area.