I have always liked The Effective Executive, by Peter Drucker.  While the book was first printed before many of the current leaders were in business, the core truths remain the same.  There is a difference between managing your organization and working in your organization.  Focusing on where you spend your time is critical.  A great leader knows how to find the strengths in people and organizations and use those to get things done.  Finally, how you go about making decisions and implementing them is critical.  If you can get past the references to IBM typewriters and female secretaries, the book remains mandatory reading for executives today.