I started writing this 3 months ago and forgot it. oops. anyway here's a few more recommendations:
Mosquito: The Story of Man's Deadliest Foe I mentioned this in a comment on firefly a few weeks ago (oops - now months again) . Its a classic tale of the effectiveness of evolution and human ingenuity as we battle to control mosquitos safely. All sorts of weird historical, biological nad trivial details are told in a calm, knowing prose style. Brillliant.
Fencing Paradise : Reflections on the Myths of Eden - This isn't about the Eden Project (of which more in due time) particularly but is more a kind of reflection on the key plants and eco-agricultural systems it demonstrates. Richard Mabey was described by the Times as Britain's leading nature writer. They're probably right. A fascinating book which gets into the ethos of Eden if not the story.
Reef Fish Identification: Florida, Caribbean, Bahamas - There are a range of these books for varying locations. These guys are real pro's and if you want to know what you saw whilst diving or snorkelling, don't bother with those pointless id slates with bad artists impressions; get a proper photo fieldguide.
The Birds of Heaven: Travels with Cranes - Chap travels the world to see all the species of Crane. Travelogue/natural history/introspective thingy. Again fantastic.