My LFS is Vang's Plakat Aquaria. He'll order me anything I need if he doesnt stock it, is very knowledgeable, and generally a great guy. He's given me some great deals before and always tries to be as personal and accomodating as possible. He also remembers almost every customer he's had, even if they dont buy anything.
I've been to other specialty aquatic stores like hoffers and Aquatics unlimited, but their prices are exhorbitant. Petsmart is my second choice. Their fish are always healthy and tanks always clean when I go in there.