From the Ashes, by Frank Zaccari, combines business concepts with some history from the University of Washington volleyball program.
Peak - Secrets from the New Science of Expertise helps you understand what the concept of deliberate practice means and how to apply it.
Barking Up the Wrong Tree by Eric Barker is an interesting combination of stories and research that could help you both personally and as a coach.
Great Teams is a book that does a really good job combining sports and business insights into a resource with a lot of good concepts and ideas.
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.
Wooden on Leadership is full of legendary coach John Wooden's insights into coaching and leadership. It's a book I definitely recommend you put on your reading list.
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.
The Coaching Habit by Michael Bungay Stanier is more a management book than a coaching one, but it provides an interesting set of questions you can use working with your players and teams.