In the process of researching for a post I’m planning on companion planting I came across a great information resource at the website of the University of Tennessee, Institute of Agriculture website. They aren’t dealing solely with permaculture or organic farming, but much of the material is very relevant to those approaches.
I’ve edited the list of topics that their website links to, to make it a bit more relevant, but when you click on any one of the links below it will put you into their whole list of topics, so you can wander through it as you wish.