A short list rather than a long one. Everything here is free unless noted, and I have actually used all of it.
Start here
Patrick Ryan — How To Make Sourdough Bread Masterclass
Hands-down the best free fifteen minutes of instruction on the internet. Learn everything you need to know including how to make a starter. You are in safe, caring hands with Patrick and his accent is lovely. A must watch!
Go deeper
The Sourdough Framework — Hendrik Kleinwächter
As it says on the site: Go beyond recipes. A complete, science-backed foundation for baking exceptional sourdough bread at home — from your first starter to your best loaf. Covers everything including all the different types of starter.
My own guide
The written version of what I teach, including the fridge-storage method that means you are not feeding a starter twice a day forever. Download it here — free, no email address needed.