lfs in Seattle:
The Fish Store on Roosevelt and 62nd - fairly cheap, knowledgeable staff, goodish selection. This used to be my first stop but the last few times I've been in they have either not had what I wanted, been rude and unhelpful or the fish have looked a bit sick. Still, if you go in the middle of a weekday they are happy to spend an hour with you chatting about your tank setup. Some of the employees are better than others. A bit snobby, they only carry what THEY think is important.
Little Amazon on Aurora and about 103rd - If you want cichlids this is the place to go. Owned by a very knowledgeable guy (his english isn't always intelligible). All of his fish are healthy and beautiful. The store layout sucks, the aisles are incredibly narrow and it's hard to find stuff. Still, he has a good selection of equipment (fewer fish than TFS) and good prices.
Petsmart on 145th & Aurora has a great selection of tanks and accessories but crappy fish. Petco on 15th where it runs into holman rd has good fish and equipment but few tanks.
There's a fish store in the University district that deals exclusively in Marine tanks and I've heard that Burien and Renton have great lfs's but I haven't taken the side trips yet.
Hope this helps.