Craig Elevitch’s Agroforestry Net, Inc. is a nonprofit organization dedicated to providing educational resources about agroforestry, trees, and sustainable stewardship of land and water. http://agroforestry.org/
Popular series of Agrodok 44 books on small-scale sustainable agriculture, published by the Agromisa Knowledge Centre for Small Scale Sustainable Agriculture, based in Wageningen in the Netherlands. The Agrodok books focus on the tropics, but the information is relevant anywhere.
Paul Wheaton’s website Permies.com. One of the top permaculture forums in the world, a wealth of resources – https://permies.com/
The PRI website is an online extension of the Permaculture Research Institute, headed by Geoff & Nadia Lawton. This is probably the largest database of permaculture articles on the world.
Plants for the Future Database
PFAF is a fantastic free online plant database with information on over 7000 edible or otherwise useful plants including their origins, place in successions, edibility and medicinal uses.
Permaculture Teaching Matters is Rosemary Morrow’s new teaching guide for permaculture teachers.