The Science of Volleyball Practice Development and Drill Design has some good information based on motor learning concepts, but is a very difficult read.
The Art of Volleyball Hitting by John L. Bowman is a quite thorough discussion of hitting aimed at players, but I think you can find far better resources.
From the Ashes, by Frank Zaccari, combines business concepts with some history from the University of Washington volleyball program.
Nikolai Karpol is perhaps best known for his yelling, but that masks a whole lot of coaching success. This book shares his ways of thinking about things.
Dream Like a Champion - Wins, Losses, and Leadership the Nebraska Volleyball Way by Brandon Vogel and John Cook is an interesting view into the mentality of one of today's most successful coaches.
A Fresh Season is Terry Pettit's second coaching related book. Like his first, it's a series of essays and other short pieces covering an array of subjects.
A Program with Purpose by Johan Dulfur is a book that shares insights and experience about volleyball team program building and development
Spike! is the story of the 1984 USA men's olympic volleyball team as told by its head coach Doug Beal. It's definitely an interesting read.