21 Irrefutable Laws of Leadership by John C. Maxwell

Tribes by Seth Godin

The 21 indispensable qualities of a leader by John C. Maxwell

The Servant: A Simple Story About the True Essence of Leadership by James C. Hunter

The Leader Who Had No Title by Robin Sharma

Primal Leadership: Learning to Lead with Emotional Intelligence by Daniel Goleman, Richard Boyatzis, Annie McKee

Leadership 2.0 by Travis Bradberry & Jean Greaves

Leadership & Self Deception: Getting Out of the Box by Arbinger Institute.

Leaders eat last by Simon Sinek

Immunity to Change: How to Overcome It and Unlock the Potential in Yourself and Your Organization by Robert Kegan and Lisa Lahey.