Your local Realtor should be aware of the tax rates including any special assesments in the communities you might be looking in.
You do have a Realtor. Don't You? If not get one;-)
It's usually a good calculation to use 1.25% of the purchase price. Here's a helpful link for you. Let me know if you have any other questions.
All the best,
Prudential California Realty
m (310) 251-7725
1.25% is a widely used estimate for CA; however, if you want property-specific accuracy please see:
"Estimating Property Taxes in CA"
Additionally, you might be interested in who customarily pays County/City transfer tax: http://docs.Steven-Anthony.com/ClosingCostsGuide.pdf