I'm not personally a big collector of art books, but there are a few books of art and photography that I have really enjoyed.
One that immediately springs to mind is Play with Your Food by Joost Elffers and Saxton Freymann. They recently followed it up with a huge collection titled Food Play, but I only have their original book. Elffers and Freymann specialize in finding the human face in fruits and vegetables. Sometimes they photograph the food as is; sometimes, they combine different food items to create a fanciful creature; and often, they carve facial expressions on the food, using very precise tools and an eye for the natural lines of the material they started with. Their best work, in my opinion, involves carving faces on pumpkins, starting with the revolutionary-yet-somehow-obvious step of using the pumpkin's stem as the nose. This book is beautiful, appetizing, and screamingly funny.
Another book I own and often enjoy is Our Hope for Years to Come: The Search for Spiritual Sanctuary, with brief devotions by Rev. Martin E. Marty accompanied by the exquisite photography of his son, Micah Marty. I could give two toots for the text by the elder Marty, frankly, but Marty the younger captures images of churches, inside and out, full of mystery, beauty, wonder, and joy.
I also have 368 Animal Illustrations from Buffon's "Natural History," containing 18th-century engravings by George-Louis Leclerc (1707-1788), a.k.a. le Comte de Buffon. These are straightforward, though perhaps somewhat old-fashioned, images of a variety of wildlife, including animals you may not have heard of. I found it very helpful in identifying unfamiliar beasts I encountered in my readings, such as the stoat, the marten (not a bird) and the fisher (also not a bird). Here is one of Buffon's monkeys.
I am also crazy about a couple other books of woodcuts, both relating to the Bible: The Dore Bible Illustrations and The Complete Etchings, Engravings, and Drypoints of Albrecht Duerer. Both books contain a wealth of black-and-white images illustrating Bible stories, combining the power of simplicity with a fascinating wealth of elaborate detail. The two masters came from different ages - Duerer from the time of the Reformation, Dore from the Romantic age of the 19th century. So, in spite of their similar medium and subject matter, they created very different works of art. For example, compare these two woodcuts of the nativity of Christ: left by Duerer, right by Dore.