For all the SoCal members, here's my two cents:
Azusa Pet--Azusa, CA has some great fish. Mostly freshwater, but does have some salt. Very knowledgeable and pretty reasonable pricing. I'm usually there at least once a week, just to see what he has new in stock. He does have some baby monsters. I saw some red tail cats, some kind of shovelnose cats (not sure what kind), and of course the oscars and pangasius.
Hacienda Aquatics---La Puente, CA. Tons of fish, really reasonable pricing. I got some 1.5" clown loaches for $3/each a while back. Really good quality.
Goldfish Plus--Covina, CA. Not the healthiest stock, but you can find the occasional steal there. Great prices for equipment though. He has almost everything you can imagine in stock. Its hard to find stuff, so if you just ask the owner (Peter) he'll tell you where it is. Equipment pricing isn't that bad--he's cheaper than most places.