There’s a lot of good material out there; here are some which have been invaluable to me. My English teacher nature dictates that I put the reference books first, but there are websites here too, if you’ll persevere.
Landscape Plants for California Gardens by Bob Perry. While this book represents a serious investment (the equivalent of 10 1-gallon natives or a nicer dinner out that I’m used to), it’s invaluable. It covers just about every conceivable plant you might consider, with updated cultivar information, extremely detailed water use information, and provides an essential guide to plant palettes to help the gardener achieve a cohesive look. So, for instance, it helped me understand why crepe myrtles would not necessarily be a good pairing with grevillea (though if that works for you, go for it, and invite me for a tour!).
Sunset New Western Garden Book. If you have to ask, you must not be from around here. Or you’re a brand-new gardener. Congratulations! This is a good book to have–a complete encyclopedia of every western plant. The only drawback is that “the west” is a big territory, so when selecting a plant, you’ll need to sift through the selections appropriate for regions not your own.
California Native Plants for the Garden, by Carol Bornstein. A nice reference book with great photographs of natives actually used in landscapes. The author is a respected authority, and is persuasive without the slightly hysterical tone that sometimes permeates sustainable gardening texts.
The Garden Spot Pretty much any major water district now features waterwise gardening help on its website; here’s a particularly comprehensive one (check out its database!)
UC Davis Arboretum All-Stars provides a list and extensive information on 100 UC-identified and tested tough, reliable California-friendly plants. Remember, though, you must always adjust for region, so like any guide, it’s a suggestion. Very worth looking at, though, as it’s not limited to natives.
Theodore Payne Nursery. They are CA native True Believers, but they’re friendly and knowledgeable and their cause is just. Worth a trip to their annual Poppy Days festival, and it’s the best local selection of natives.
Las Pilitas Nursery. Their website is hands-down the best place to get educated online about natives; the writing is knowledgeable and often hilariously opinionated. Their nursery is a little out of the way, but I’m not sure they’re all that glad to see visitors, anyway, and you can order plants through the mail.