Prior to reading this thread, the only one I had heard of was Annapolis Homebrew although I've never been to it yet.
I used to live out in Washington State, and I visited Homebrew Heaven and bought a lot of equipment there since their prices are awesome...once I moved here though, I found out they don't have great shipping.
I just ordered a lot of new equipment from Austin Homebrew supply (Austin Homebrew Supply
) and they have free shipping on orders over $100, or $7.99 flat rate.
I'm definitely going to head over to Frederick one of these days though - that sounds like it might be a really neat shop.
I should visit Annapolis Homebrew soon as well since it's so close :-P