Deadly karate Blows: THe Medical Implications is an excellent book. Although not Kenpo Karate specific persay it is written by an EP black belt. Great book.
Mastering Kenpo: The Path to Excellence and Encyclopedia of Kenpo IMHO represents two key texts for American Kenpo providing any student a better understanding of the philosophy and logic of the art.
Infinite Insights Volume 5 is great because it provides a student with examples of the traditional exercises of Kenpo (forms, freestyle, and self-defense) as well as the how and why they where constructed.