This list is growing. If I missed a great one, please tell me in the comments below.
Attitude
As a Man Thinketh by James Allen
How to Win Friends and Influence People by Dale Carnegie
Little Gold Book of Yes! Attitude by Jeffrey Gitomer
Think and Grow Rich by Napoleon Hill
Today We Are Rich by Tim Sanders
Leadership
The Contrarians Guide to Leadership by Steven Sample
Drive by Daniel Pink (Read My Review)
The Five Dysfunctions of a Team by Patrick Lencioni
Good to Great by Jim Collins
How the Mighty Fall by Jim Collins (Read My Review)
Switch by Chip and Dan Heath
The 21 Irrefutable Laws of Leadership by John Maxwell
Small Group Ministry
Connecting in Communities by Eddie Mosley (Read My Review)
Prepare Your Church for the Future by Carl George
Small Groups with Purpose by Steve Gladen
The Search to Belong by Joseph Myers (Read Why I Hate Joe Myers’ Book)
Spiritual Growth
The Divine Conspiracy by Dallas Willard
Emotionally Healthy Spirituality by Pete Scazzerro (Read My Review) 
The Good and Beautiful God by James Bryan Smith
Let Your Life Speak by Parker Palmer (Read My Review)
Plan B by Pete Wilson (Read My Review)
Primal by Mark Batterson (Read My Review)
