There are a ton of free E-books to download on the Internet (and considering how little electrons weigh, a ton is a whole heck of a lot), and many of them pertain to the topics I cover in this blog. There are two ways to approach this bounty: one is to provide long lists to download en masse, and the other is to review them one-by-one. The major advantage of the first is that you have all the information if you lose access to the Internet; the main disadvantage is that you won't go through them when you download them, so you'll need to discipline yourself to come back to them later.
Since a number of people have already done the first option, I will not be doing it here. I will, however, provide links to those links and even repositories. Instead I will be providing links to individual e-books in the same annotated manner I have been for articles, videos, and everything else.
The first free E-book comes from MidwestPermaculture.com: Plant Guilds. This is a bit of a "cheat sheet" for doing permaculture in temperate climates, having done some of the design work for you. In it are 10 plans of plants that go together. Most of them are labeled by the largest tree in them; the two notable exceptions are the Bee Guild, to attract pollinators, and the Wet Meadow Guild.