Jeff Cox's book is a must have if you are trying to design plantings that really look natural. I was inspired by a few of the photographs of sculpturer Hand's work, showing the artist's inspiration in nature. Does a good job of suggesting alternatives plants for those of us with less ideal climates.
Still in the process of reading this book, but I am enjoying his approach to designing your own natural landscape. He leads you through the process by giving examples of his own experience. He teaches you how to see what is naturally there and how to recreate the same feeling if not the exact landscape.