Burbank House of Hobbies is the best. ~15 minutes from downtown L.A. in Burbank CA
. They have a great selection and the best service. Also, they have large cabinets where yoou can see several past and recent releases by Gemini, Hogan, Herpa and Dragon mainly.
But here are also a couple I visit from time to time:
Brookhurst Hobbies in Brookhust Ave (?) near Anaheim on the 22Fwy. However, their selection is limited and several of their models are old. They have actually downsized their stock recently.
Morgan's Big Train Emporium. This store is off the 401 Freeway in Huntington Beach. Direct access from and to the airport (15-20 min). This guys is very well stocked although his models are not in display, rather they're store in a back warehouse making it a bit difficult to appreciate different models.
I hope this helps.