'The First and Last Freedom' by J. Krishnamurti: Mainly because of what he says regarding Free Will. Later I read 'Free Will' by Sam Harris, and I think Sam explains the same idea in more detail.
Citing 'The First and Last Freedom': "Thought is nothing else but reaction; thought is not creative."
'The Grapes of Wrath' by John Steinbeck
'The Little Prince' by A.S.Exupery: when I was a child it made me reflect about society.