As mentioned above,
Shadow Divers and
The Last Dive are good reads; I enjoyed both.
Dangerous Marine Creatures is accessible to the layman, but provides guidance to the clinician as well, using actual case histories of bites, stings, envenomations, and poisonings. It appeals to my morbid curiosity as much as to my intellectual curiosity and, of course, has useful practical information:
Amazon.com: Dangerous Marine Creatures (9780941332392): Carl Edmonds: Books
I don't plod through books. If it doesn't engage me I abandon it. These two are not about diving, but might appeal to divers. And they read like novels:
12 Days of Terror, about the Jersey Shore shark attacks in 1916, is interesting from a few different perspectives: morbid curiosity (again), historically, and as a critique of journalism and science. It's also as suspenseful as your favorite slasher movie:
Amazon.com: Twelve Days of Terror: A Definitive Investigation of the 1916 New Jersey Shark Attacks (9781585742974): Richard G. Fernicola: Books
In Harm's Way is a great account of the sinking of the USS Indianapolis that many of us first heard about from Quint in
Jaws. More morbid curiosity, and an important historical event. It's like reading Tom Clancy, but it's non-fiction.
Amazon.com: In Harm's Way: The Sinking of the U.S.S. Indianapolis and the Extraordinary Story of Its Survivors (9780805073669): Doug Stanton: Books
Fish ID books (or software) are indispensable to me. Here are my favorites:
This one is comprehensive and, perhaps counter-intuitively, the drawings are often superior to photographs in deciding between related species:
Amazon.com: Coral Reef Fishes: Indo-Pacific and Caribbean (9780691089959): Ewald Lieske, Robert Myers: Books
Whatever the appropriate book by Humann, Deloach is for where you dive:
Amazon.com: The Reef Set: Reef Fish, Reef Creature and Reef Coral (3 Volumes) (9781878348333): Paul Humann, Ned Deloach: Books
The collaboration between the two great fish-identification teams, Humann, Deloach and Steene, Allen:
Amazon.com: Reef Fish Identification - Tropical Pacific (9781878348364): Gerald Allen, Roger Steene, Paul Humann, Ned DeLoach: Books