A couple of these have been named and I've upvoted them, but this is my list:
* "Flow" by Mihály Csíkszentmihályi. Being fully immersed and engaged in an activity. 1) Knowing the value of this mental state, 2) being able to recognize when you're in it, and 3) setting yourself up so that you can be in this state as much as possible is really valuable. File it under living an examined life, IMO. All the popular "don't interrupt the programmer" and Pomodoro and other time management techniques build on this old research.
* "Meditations" by Marcus Aurelius (several translations, worth comparing for even more insight) -- this is a man who understood duty and getting things done! (Not surprising from a stoic, but somehow this collection has extra impact because I know they were primarily notes and reflections written for his own clarity, more than for an audience.) Wisdom to apply to situations. Patterns to recognize in yourself and others.
* "Seven Habits of Highly Effective People" by Stephen Covey. When more sophisticated or trendy approaches to effectiveness reach their limits, you can't go wrong falling back on "Begin with the end in mind", "Sharpen the saw", classifying activities into the Four Quadrants, etc.
* Modern (typically psychological) interpretations of Buddhism. If a single book pops into my head, I will update this, so right now I'm talking about a whole category of books on Buddhist perspectives on character traits and habits of behaviour. If you strip any paranormal nonsense from Buddhist psychology you are often left with effective ways to classify your own thoughts, words, and deeds and work on improving them. A simple example would be the Four Sublime Attitudes. If I reflect on any relationship or interaction I have with colleagues or clients or new prospects, I can almost always take direct action immediately to improve it by applying these old rules: 1) replace anger toward someone with active good will toward them, 2) replace jealousy or envy of someone else's fortune with sympathetic joy for them, 3) approach anyone's suffering as your own suffering (compassion), 4) treat all situations and people impartially without judgement of of "good" or "bad" (equanimity).
I'm sorry these are really old! For me, these just don't go out of style and their wisdom works cross-culture.