I have experience with 3 of them.
Marine Scene in Herndon, SuperPetz in Annandale and Congressional Aquarium in Rockville.
Marine Scene has decent corals, but every fish I've ever bought from them has Ich, the dry goods are pretty expensive. They're the most knowledgeable, but common sense still applies when taking advice from them. It used to be much, much better, but its still not bad.
Superpetz has cheap tanks and drygoods, not a lot of fish which tend to be hit or miss and more or less no corals.
Congressional has cheap salt (like $14 a bag IO cheap salt, all the time), thats about it. Last couple times I've been in there the live stock hasnt looked so hot.
There's another place in Annandale called Wally's Aquarium, which I went into once, and pretty much walked right back out of.
If you want a road trip (its worth it), go to Pacific East Aquaculture (aka Dr. Mac's) outside of Salisbury Md. Its probably almost a 3 hr drive, but he's got more gorgeous stuff than you could ever want.
