name   The Bass Handbook of Leadership
author   B.M. Bass
year   2008 (4th edition)
pages   1536
THE handbook of leadership research and theories. An exhaustive collection of pretty much everything leadersip-related under the sun. Like Industrial Bookshelf editor said: " It is an antidote for books of speculation and personal opinion that often mislead a manager more than help him."

This is the solid ground, the cornerstone. Standing on this a leader is much better off than on any thumb-method opinions. But its a daunting read, and more of a lifetime project and a reference book.