While it isn't about volleyball, The Inner Game of Tennis is a classic book about the athlete mind and how to progress toward optimal performance.
Here's my review of Kathy DeBoer's book Gender & Competition, which takes a look at how men and women view things and act in very different ways.
Although it didn't alter my thinking on coaching the way it may have done for some others, I did find Sacred Hoops to be a good coaching book read.
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.
My Profession - The Game is the English translation of the last of several books written by legendary Russian volleyball coach Vyacheslav Platonov
Although there are a few interesting elements and worthwhile anecdotes, overall this is not a volleyball coaching book I am inclined to recommend for reading.
Winning Volleyball is a book of its time in that is doesn't reflect the modern game in many respects, but it's not without value to current volleyball coaches.
Volleyball Skills & Drills is a book by the American Volleyball Coaches Association featuring a ten useful chapters on the various aspects of coaching the game.