I'm not much of a reader, and certainly not much fan of fiction/fantasy the way I used to be. Some, but not all books have stood out though:
Slaughterhouse 5
Unknown Soldier
Zen and the Art of Motorcycle Maintenance
(yeah I did read Tolkien a LOT some 20-25 years ago but those books are not on the list as I don't read that stuff anymore)
But the books I enjoy the most now are books like
L
onely Hearts of the Cosmos
The Code Book
and one by Nils Mustelin, English title "Life In the Universe?". Books that invite to a bit of thinking can't hurt.