This is a gorgeous book with many large, full-page color pictures of gardens in various styles (both formal and naturalistic). The author is a well-known British garden expert, so the discussion has a British slant, but I found it useful and inspiring nevertheless. Sections include:
Flowers in detail
The palette of flowering plants
The natural garden
The flower border
The framed garden
Plants for the flower garden: an A-Z guide
Chapters include information about garden design and maintenance, as well as features from impressive private and public gardens in Western Europe and the U.S. Eminently drool-worthy.