My own LivingJoy material is my favorite, and not because I created it. Rather, because it is based on 40 years of personal growth and research, learning from the best of the best.
However, it is not yet published - keep an eye out for an announcement within a year!
In the meantime, I believe the deepest and most valuable works of the past 50 years are: The 7 Habits of Highly Effective People (see my series of hubs on that topic); The Artists Way, by Julia Cameron; and Grow Rich With Peace of Mind (not the earlier Think and Grow Rich) by Napoleon Hill.
Note: These are not for the browse-and-look-for-more readers. These are for people who want to transform themselves and become happy, creative, productive people who make the world a better place.
First read, then do!