On an earlier posting, maifleur made a very important point about the fire risk associated with native plants in your particular area. I would definitely keep this in mind when planning any landscaping. Artificial irrigation will be required no matter what you plant in your area.

As maifleur mentioned in her post, it may be that native plant landscaping may just not be practical or safe in your area, especially in close proximity to your house.

Since fire is such a serious issue, I would consult with a local professional organization about your landscape plans.

You can contact the Orange County Fire Authority, or your local fire department to see what they recommend as far as landscaping and fire safety:
http://www.ocfa.org/

There's an organization called the Firewise Community that I would also check out:
http://www.firewise.org/

Here's a web page about fire-resistance and Orange County:
http://www.firewise.org/resources/everyones_resp/orange_county.html

The Orange County Native Plant Society may also be of some help:
http://www.occnps.org/

You may also want to post the question regarding your lawn replacement project on the GardenWeb's "California" forum, and see if anyone on that forum has suggestions for fire-resistant landscaping.

Hiring a professional landscaper that will assist you with creating a fire-resistant landscape plan may also be helpful. Sometimes landscapers will be open to being hired for consultation only, and then let you install the plants yourself, which can save you some money.

Hopefully through some research, you will come up with a landscape plan that is fire-resistant, eco-friendly and easy to care for.