I have made some awesome sourdough from the recipe in "The Breadbaker's Apprentice" by Peter Reinhart. I also make a lot of the Pain l'Ancienne baguettes. You will not be sorry you bought this book.
He simulates the wild yeasts from the San Francisco area by soaking California raisins in water to make a starter. Pretty slick, and cheaper than having to import dried cultures.
I have actually heard of this recipe growing up in the Bay Area. My mother loved to experiment with bread recipes and it really does help make a great sourdough!!