There are a number of books that cover the history of garden design, which offer excellent inspiration for contemporary designs, including "Paradise on Earth: The Gardens of Western Europe," and "Icons of Garden Design." A large number of these books contain illustrations and photographs.
The book "An Illustrated History of Gardening" provides some interesting insights into the activity of gardening itself, as well as offering useful information on the basics of garden tools and techniques.
"Gardens for the Future: Gestures Against the Wild" offers examples of more contemporary garden designs taken from around the world. The many photographs in this book make it a great source of inspiration for modern design ideas.
There are also a number of books that examine the garden designs of Europe and America, with numerous illustrated and photographic examples. Some titles include "Arts and Crafts Gardens," which deals with the historic garden designs of Britain using a large amount of illustration, "Renoir's Garden," an illustrated account of the famous French garden at Giverny, and "The Golden Age of American Gardens," which examines the garden design trends of American gardens from 1890 to 1940.
More specialized texts with full illustrations are also available, covering such topics as the use and design of garden ornamentation from historic times to the modern age.