I think "How To Make Knives" by Barney and Loveless is still the bible of this craft, but I have other books that offer different things. The "Gun Digest Book of Knifemaking" is really good for very basic stuff, showing the authors' experience with kits and simple customs before moving to an overview of custom knifemaking that includes very little "how-to." David Boye's "Step-by-Step Knifemaking" has tons of info on a variety of methods of knifemaking that are less common, as it largely details making knives from saw blades, but it is a huge, info-packed book that I feel any knifemaker could benefit from. Finally, "How To Make Folding Knives" by Centofante, Clay, and Lake is a great look at three different approaches to classic lockbacks, but will tell you little about more modern folder styles, except basics that all folders share.
OK, that's a long answer. "How To Make Knives" is my favorite, that's the short answer.
(Why else would a bear want a pocket?)