"Lizards of the World" by Chris Mattison amazed me with all of the excellent information in it. It contains everything from the scientific (scientific names/family trees, scale types, graphs, diagrams, maps, and pictures) all the way to recommendations for future lizard pet owners.
It talks about all the different types of lizards, from four-legged flying types to legless and amphisbaenians (worm-lizards), in great detail while supplying pictures or diagrams on almost every page (some pictures are in colour while others are in black and white). Chris Mattison talks about lizards and their form and function, food and feeding, defence, reproduction, habitat, lizards in captivity (information for future lizard pet owners), classification, and their different environments.
I am a reptile fanatic, and I have been a reptile fanatic for as long as anyone can remember, and I have yet to find a book that can out beat "Lizards of the World" for the most overall best information on lizards. It is also worth to mention that I have searched a long time trying to find a perfect lizard book, and this book reaches all of my expectations and more.
I do warn you, though, that this book is not new (it was first published in hardcover in 1989) so it is possible that some information is out of date. But, overall, it contains information that is helpful no matter what year it is: it gives more general information rather than things specific to a certain year. The only thing that might be different is some of the numbers regarding the amount of known species and some of the diagrams.
I would recommend "Lizards of the World" to any lizard fanatic. It is a perfect companion to be used as a reference and it is a good gift idea.