With hackers and crackers and other prying eyes trying to intercept and view your sensitive or confidential information it is becoming more and more important to ensure that only those intended to see it get to see it. Using encryption and cryptography you can scramble your documents and messages so that only the intended recipient can view it.
This is more a book of theory and opinion- but a good one at that. At times, because they do put some math and pseudocode, it may get a little techie for the general audience. It provides a good introduction to cryptography and walks the reader through various types of cryptography and how they are flawed. You can't take one part of security out of context and be secure.
Eric Cole has a background in working with hidden data and his experience is translated into a book that even users new to the concepts of covert communication can understand. The book covers a basic history of cryptography as well as steganography and then gets into more detail about the techniques and concepts of "stego".
PKI Security Solutions provides a good introduction to the concepts and technology that make up Public Key Infrastructure solutions. It helps administrators design cost-effective solutions to protect their Internet communications. The case studies help readers to put things in perspective and grasp the concepts more quickly.
Adam Young and Moti Yung provide a glimpse at how malware development might be combined with cryptography and what sort of malicious code could result.