Napolean Hill's writing is to Personal Development what the Gospel of John is to Christianity.
Hill was quite daring for his time, and should be required reading for every high school student. The idea that we become what we think about seems so... common, yet the implications are earthshattering. Prior to that, success literature was focused on changing our circumstances... work harder, save money, be a saver. All good advice, but Hill showed us that we could change ourselves.
The Laws of Success is definantly the way to go, as Think and Grow Rich was written to be a popular introduction for the masses. Much more detail is available in the LOS.
It is also interesting to note that Hill spoke of such things (without using the names we now have for them) as Out of Body Experiences, Guides, Channeling, and the Collective Unconscious.