Although I am an avid reader and have been reading on average 1 or 2 books each week for the past 15 years, I don't think I've ever read a book than "changed my life". Looking back, I think the most impactfull book for me was The Art of Loving (1956) by Erich Fromm because it opened up a world of psychology and psychoanalysis and significantly altered my view on how humans think.

Among the classic fiction the best so far were: T. Dreiser - The Bulwark, S. Maugham - Of Human Bondage, L. Tolstoy - The Kreutzer Sonata and E. Zola - l'Oeuvre & Germinal.