Albert Camus
The French existentialist writer Albert Camus, even more so than other French thinkers, has challenged what it means to be a human being after Auschwitz. His plays, novels, and essays have shaped my own post-Auschwitz outlook on life more than any other person, save perhaps the French philosopher Emmanuel Levinas.
Camus challenges us to re-think our values and assumptions about the very basic components of life such as responsibility, happiness, and duty. Though so many find such a negative, even nihilistic strain in his and other existentialist writings, I find no such notions. His writings point one in the direction of recuperation and healing in the face of such cold realities like the holocaust and man's inhumanity towards man. It is just that the kind of healing we need is not at all what he had in mind. Like couples going to their first therapy session together, they know what they want to hear. Then they get the truth. And as Camus shows us, the truth is never easy to take.
A very good, exhaustive site on Camus' work: http://www.mythosandlogos.com/Camus.html
A good primer on Existentialism: http://www.tameri.com/csw/exist/camus.shtml