I didn't see this mentioned below, so keep it in mind. The assessor/County will have a record of the current tax basis --- not the one you would necessarily have when you purchase the home. Upon transfer (title going from seller to you, the buyer) the home will be reassessed using the purchase price. For this reason, we use an estimate of 1.25% of the purchase price (divided by 12 to get your monthly equivalent tax amount). If there are other taxes you need to consider, the assessor's info will help with that too.
In short, I would ask your real estate agent to get you a firm idea. He/she should be very familiar with what to expect.
An explanation of the Property Tax bill can be found here: http://www.ventura.org/ttc/secured-property-tax-sample-bill
For those so inclined, they even have a FaceBook page: https://www.facebook.com/VCTreasurerTaxColl
1.25% is a common "quesstimate"; however, your effective property tax bill actually consists of three separate levy categories: General Tax Levy, Voter Approved Indebtedness and Direct/Special Assessments.
See: "Estimating Property Taxes in CA" http://tinyurl.com/bjjledz for a thorough review.