California is a big state, with ecosystems ranging from sand dunes to desert, forest, shrubland, and swamp. The most water-wise plants for any garden are those that have evolved naturally in the local area, with the added benefit that they help to support local native pollinators too.
All of the plants pictured in the following lists grew at the Bernard Field Station in Claremont without any water other than what nature provided. (However, your garden plants are more likely to succeed if they are given some water to help them get established, and most will benefit by a monthly watering in the summer.)
Possible sources for these plants are the Grow Native Nursery at Rancho Santa Ana Botanic Garden and the Theodore Payne Foundation, and some can be found at ordinary nurseries.