Spotlight on Sourdough
Certified Executive Pastry Chef and Certified Culinary Educator carltonb has provided some wonderful information on baking with sourdough. There are three parts:
There is a pictoral essay  on the steps involved in the development of a starter culture.
Next there is a feeding chart  that provides details behind the pictures in his essay. Scaled down, this provides an excellent formula that a home baker could use to create a starter culture.
Finally, Carlton shared an outline of a presentation on the sourdough process . There are some excellent summations in here; if I have any complaint it is that I wish I could hear his entire presentation!
Be sure to catch the diagrams at the bottom of the outline. They are extremely helpful.
I should warn that home bakers just getting started with sourdough might find these articles a bit daunting: Carlton bakes at a level and has an understanding of these processes far more advanced than I do. Don't be scared away! There are a number of other articles about sourdough and starting a culture on this site  that I suspect are more approachable to beginners. Once you've got a starter going and want a deeper understand of what is going on, come back to these because they are chock full of useful information.