Hard to say.

We the Living by Ayn Rand. An interesting story that also offered a glimpse of what living under communism was like.

The Lion, the Witch and the Wardrobe or Wrinkle in Time, because it captured my imagination as a child.

Any number of sci-fi books by P. K. Dick, Tolkien, or Isaac Asimov, who created worlds.

The Jungle, which sparked change which effected US agriculture industry.

I feel like I could go on and on. It's an impossible question.

Several years ago I read "In the Heart of the Sea" (the Moby Dick story) and I still think about it frequently. You learn about the old whalers, then the whale hunts the whalers, starvation, cannibalism, then the guys who made it out alive went out and did it again.

https://en.wikipedia.org/wiki/In_the_Heart_of_the_Sea

For some reason, I still haven't seen the movie... Chris Helmsworth, maybe.

Although it wasn't as entertaining as other books I've read. I'd have to say The Art of Asking by Amanda Palmer. Its half biographical and the other half is made up of tangents. But the main theme through out is basically the closed mouth doesn't get fed. It's not necessarily a self help book by normal standards. But it had quite a few points that helped inspire me to grow and better myself as a person. Such as overcoming the inability to actually ask for help when needed. Most people are willing if you just simply ask.

Not one I'd reccomend to the regular crowd associated with forum boards like this. But it's certainly had more of an impact on me than any other book.

Too many too mention and for different reasons.

I remember really like the way De Camp wrote the Conan novels, and being disappointed on reading the Jordan(Wheel of Time series) continuation of them. I think I'll chase that book up after I get my current crop out of the way. I've long held the belief that we modern humans underestimate the intelligence and ability to problem-solve of others including ancient humans and some animals.