Here are a few links where I've adopted cats before.

Humane Society This is my local Humane Society and I adopted both Storm and Sky from here.

Friends Of San Martin Animal Shelter I adopted Starr from a woman who worked with this shelter group.

Stanford Cat Network This rescue group helps homeless cats at Stanford University. I adopted Cirrus from them. Most of their cats are ferals or semi-feral.

Here's a link in adobe format that lists California rescue groups: CA Rescue Groups Master's List I adopted Sunny from Unconditional Love but they don't have a website right now.