How to Win Friends and Influence People, Dale Carnegie
The Lean Startup by Eric Ries
The Innovators Dilemma by Clayton M Christensen
Freakonomics - Steve Dubner
Richard Potter, Director of Digital Strategy, Microsoft
Scaling Up, by Verne Harnish
Better Managers = Better Business, by Pete Fullard
McKinsey Quarterly (a wide range of leadership, management and strategic thinking)
Harvard Business Review (a wide range of leadership thinking)
David Clutterbuck (a good resource for coaching and mentoring thinking)
William Buist: Intentional Mastery
Stephen Covey: The 7 Habits of Highly Effective People
R. Michael Anderson: Leadership Mindset 2.0
Nick Howell: Great Coaching Questions
Nancy Kline: Time to Think