If your board is an average design without micro vias, I can recommend Alltek - a small company in Irvine. They are honest, they'll work with you on price, and they do a good job. If you ask, they'll give you a tour of their facility - https://www.alltekcircuit.com/ .
If your board needs micro technology, exotic substrates, or unusual machining I would recommend either Dynamic Details (expensive) in Anaheim, or Gorilla Circuits (not in SoCal, but they ship overnight anywhere in the US). **broken link removed**
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One of the oldest companies in the area is Alphanetics in Santa Ana. Like Alltek, they can handle standard board technolgies. They do a lot of boards for commercial manufacturers. They're competative on price - **broken link removed**