First one is if you sign-up to the newsletter at Soulpods.org you get to download their Sustainability Collection which includes ebooks on organic gardening, fertilizer, bee farming, and starting a small scale farm. Soulpods Sustainability Freebook Collection < -- you need to wait for the fly-over box to appear and input your email address to receive them.
There's also a really great ebook on Aquaponics at IBCofAquaponics.com
Also for those that are in countries where it is legal, I would recommend searching on torrentz.eu or another torrent search engine for any topic of alternative building (rammed earth, cobb, superadobe, etc.), sustainability, permaculture, gardening etc… you’ll find a lot of resources to download. 😉