I have started a sourdough starter! I started it on Sunday, so far it is going well and I had bubbles last night. I am probably too excited about it. Hopefully I can make some sourdough over the weekend.
This blog post from Joy the Baker is super useful, some of the other recipes out there are ESSAYS on the subject, really it is simple. One cup of bread flour. One cup of water. Blend. Every 24 hours for the first 3-4 days you need to feed it. Do this by throwing half away, and adding half cup of water and half a cup of flour. Stir. Leave in a warm place. Once it has established itself you keep it in the fridge and feed it once a week.
(if anyone knows how to take an attractive picture of this big yeasty floury mess I'd be grateful, haha).