In no particular order:
San Diego Zoo
San Diego Sea World
San Diego Wild Animal Park, while they still had the monorail. I don't care for the
renamed SD Safari Park. Now you can't see the majority of the animals. I don't know
if they still have them, or not.
Los Angeles Zoo (prior to 1990)
Denver Zoo
Fresno Zoo (smaller, so easier on the tootsies)
Santa Barbara Zoo (tiny, but right by the Pacific Ocean, and gorgeous)
California Living Desert Museum (by Palm Springs- the zoo has fascinating
and unique desert species from around the world, including the Mexican wolf
and the addax antelope)
Phoenix Zoo
Lima Peru Zoo (their herds of white-lipped peccaries and capybaras were
fascinating, and they had other animals unique to that country)
Hogle Zoo
Willow Park Zoo- Logan, Utah (the zoo is tiny, but has a very nice
pheasant collection, an albino porcupine, coatimundis, and fallow deer)
I like all zoos, because there are cool animals and usually plants in all of them, no matter how small. Small does not have to mean bad, and big doesn't always mean good. Every zoo is flawed and could improve, and every zoo has good points.