I've read Native American's washed their hair with wood ash. I haven't tried it, but I am curious. I use a natural shampoo right now. I am also in the process of creating dreadlocks in my hair so it is easier to maintain.
My husband tried the water only thing and his hair was extremely greasy. He kept saying it would eventually balance out, but he couldn't wait much longer, I feared his job would start to ask questions and he already has a pretty crazy beard that was pushing their limits of what "professionalism" should be.
I have tried the baking soda vinegar thing and I never did it long enough to notice if it would work long term or not. Right now, I need to keep my hair very clean and oil free so the dread can tighten up.