For fish, blue zoo hands down; liveaquaria/diver's den was bought by petco. I've gotten good corals from Unique and The Salty Underground. On eBay: SoCal Aquafarms.
The quality of LA DD hasn't changed since Petco bought them. There is a sticky addressing the issue. LiveAquaria and Divers Den still provides excellent quality fish, and amazing customer support. BlueZoo and LiveAquaria are pretty much the same as far as quality of fish, but LiveAquaria does have better customer service.
KP aquatics, best live rock in the USA, no mobile hitchhikers just fantastic colorful live rock.
Just got an order from Pacific East Aquaculture. HUGE selection and great prices. Was my first time ordering livestock online and it went well. Just wish overnight shipping didn't cost so much.
X2, If you are in their zone 1 shipping area you can not beat it. Outside of that they still get in some very unique pieces.