Gaias Garden by Toby Hemenway is a very comprehensive book on permaculture. The book is neatly divided in sections so you can look up the information you are interested in. The first time I read the book though, I read it from start to finish. Later on, I reread important sections and looked up things again. And I still refer to the book when I am stuck on something. I especially find the plant lists very useful!
Part One looks at the garden as an ecosystem and gives an overview of what permaculture is. It also compares permaculture to more traditional types of gardening, and looks at the differences between a mature and an immature system. Then it coves some of the typical permaculture garden designs, touches upon guild planting and goes over the zones used in permaculture.
Part Two goes more into detail on the different parts of an ecological garden. It covers everything from building soil to water catchment and conserving to how to use plants for multiple purposes. It also looks at how other creatures like birds and insects interact with the garden.
The last part, Part Three, goes over how to assemble the garden. Here we learn how to create plant communities, or guilds, and how to go about creating a food forest. This part of the book also has a section about permaculture in the city, which is becoming more and more relevant.
All parts of the book has lots of examples and inspiring photos to see practical examples. There are illustrations and lots of tables with different plants and what goes with what.