The Absolute at Large and War with the Newts by Karel Čapek. These two books triggered a mental avalanche. Though it was a set of circumstances I was flaoting in when I read them. Karel Čapek was the writer who coined the term robot though it was suggested to him by his brother Jospeh. Rossum's Universal Robots was apparently the first time the term was used in a literary work. Until reading War with the Newts I was always reluctant to engage in implausible stories.

If you meet the bhudda on the road kill him - sheldon kopp

The Structure of Scientific Revolutions by Thomas Kuhn. I read it as an undergraduate. It was the first time that I read anything that indicated that the sciences were not as objective as advertised. None of my teachers before had dealt with this topic, and certainly not my father the physicist.

Short story actually, Rage by Stephan King. (Richard Bachman at the time)

Joseph Andrews, by Henry Fielding. As a teenager if influenced me greatly, and cristalised my hatred of affectation which I harbour to this day.

The first book that changed my mind about how I perceived the world, was a very small book.
Thoughts are Things.
I am sure I still have the original book.

Why I am a Unitarian.

Five Ages of Man.
Twelve year cycles that we all go through. Once I attained the 5th cycle, I thought there should have been extended Ages. The Author may have only expected to live just so long. Very interesting.

I'm not trying to be funny but it was a comic book. I went from door to door pulling a wagon and asking people if they had any newspapers or magazines they wanted to get rid of. A friends dad would take our haul down to the Rag & Metal and we would make a few dollars. Well it was an Archie comic book that lit the fire for reading. I read incessantly through most of my life. I believe it taught me to be articulate and expand opportunities throughout life.

“There are two ways to slide easily through life: Namely, to believe everything, or to doubt everything; both ways save us from thinking. The majority take the line of least resistance, preferring to have their thinking done for them; they accept ready-made individual, private doctrines as their own and follow them more or less blindly. Every generation looks upon its own creeds as true and permanent and has a mingled smile of pity and contempt for the prejudices of the past. For two hundred or more generations of our historical past this attitude has been repeated two hundred or more times, and unless we are very careful our children will have the same attitude toward us.”
― Alfred Korzybski, Manhood of Humanity

The Tyranny of Malice - Joseph Berke

A Wrinkle In Time I read it as a fourth grader.

Many years ago I purchased something called The Neo-Tech Discovery Manuscript. It has much in common with objectivism and even references Rand, if I recall correctly. That got me interested in her works so I started with Atlas Shrugged and went on to read most of her body of work, both fiction and philosophy. Those materials, combined, helped to change my thinking and to solidify my Atheism as well as my support of Laissez-Faire Capitalism.

There have been many.
But "The Teachings of Don Juan, A Yaqui''s Way of Knowledge" --- Castenada --- might be the top one. I read it while decompressing after a tour in Vietnam. I was stationed in Southern Arizona and spent a lot of time "south of the border".