Combining my two biggest hobbies, gardening and reading, I felt like listing some of my favorite gardening books.
Passalong Plants by Steve Bender and Felder Rushing. The book has a lot of humor and is a very easy read. Although it lists plants that grow in the Middle South, I've gotten a fair number of the plants they recommend which are hardy in Zone 6.
The Fragrant Path by Louise Beebe Wilder. I have at least three copies of this in different editions, and have given another copy away as a present. Mrs. Wilder writes absolutely lyrically about wonderful plants for a fragrant garden. I've read the book so many times that I practically have it memorized, and I've gotten as many of the plants she mentions as I could collect.
A Southern Garden by Elizabeth Lawrence -- and really, any other of Elizabeth Lawrence's books. She's a wonderful writer with a very conversational style, and gives so much information about the plants and about garden design.
Landscaping with Antique Roses by Liz Druitt and G. Michael Shoup. Absolutely gorgeous photographs and a wealth of information about some lovely Old Garden Roses. I wish I could grow the China, Tea, and Noisette roses here, but they also describe some Gallicas, Albas, Damasks, Bourbons, and Hybrid Perpetuals. I've collected as many of the hardier roses as I could afford. Actually, more than I could really afford, but that's another story.
African-American Gardens and Yards in the Rural South by Richard Westmacott. This gave me so many ideas about the kinds of gardens you could grow if you don't have much money, but have a lot of creativity. There are some wonderful photographs here, and the text is quite evocative as well.
Theme Gardens by Barbara Damrosch. Gave me ideas about researching historical styles of gardening. My gardens don't really have themes, but I have tried to acquire some of the plants which were grown in antiquity and in various historic eras. I have a good number of Victorian-age roses, for example.
The Cottage Garden by Christopher Lloyd and Richard Bird. Fantastic photographs and great descriptions. Full of information, much of which can also apply to American gardens.
In the "collect as many of his or her books as possible" category, I've already mentioned Elizabeth Lawrence. I also recommend Graham Stuart Thomas, especially his books on roses.
I'll edit this list to add other favorites, but these are some books which have been favorites of mine for years.