The first was Peters and Waterman, In Search of Excellence. The second was Senge's, The Fifth Discipline. The one now is Who Do You Want Your Customers to Become? Going through those books I would read a sentence or two and would have to put the book down and think through how to use what I was reading. All of those books are business books. My application was being more effective in ministry.
So what is a good book? One that challenges your thinking, one that suggests action that you see you can take immediately. I have a stable of authors that do that for me now, Kotter, Gladwell, Godin, to name a few. All these are filtered through the hours of Bible study I do each week. But as I have written before, truth shows up where it does, Matthew 5:45.