I've heard a good deal about Santa Barbara Orchid Society. The society I just joined took an excursion down to SBOS a few months ago, and I've heard good things.
Another place, about 1 1/2 - 2 hours from L.A., is
Andy's Orchids . He especializes in species. I haven't been to his nursery, but have ordered from him and spoken with him over the phone...very helpful and knowledgable. The plants I bought from him are good quality. So if you don't mind taking a drive down (and do some sightseeing on the way
), I recommend you visit his nursery. When you return home, let me know if you do and tell me about it.