A few of my favorites:
The Reef out on St. College Dr. in Anahiem (Everyone should have been to this one)
Tong's in Whittier on Whittier Blvd (Lady there kinda rude)
Fish Etc. in West Covina
ALl Happy in Monterey Park (Good luck finding them open)
Tropical Fish House on Holt Blvd in Montclair (Terrible Customer Service but koo fish)
P&P Tropical Fish on Ball Rd in Cypress ("hole in the wall" place but awesome prices)
Goldfish Plus on Grand in Covina (Has larger sized fish)
Deep Sea Creations on H79 in Temecula (New Place but has had a few interesting fish : Large Electric Eels, Mbu puffers, Arrowhead puffers, Huge Ropefish/Reedfish, Baby SW Barracuda, Nautilus, different types of Stonefish, Scorpionfish, & Toadfish, etc.)