A couple years ago I read a biography on the life of Koestler titled, "Koestler: A Biography" by Iain Hamilton. Koestler is most famous for his novel, "Darkness At Noon" which I read in High School. I am still looking for a used copy of the novel "Darkness At Noon".
Arthur Koestler Collection
"The Yogi and the Commissar and other essays" by Arthur Koestler
"Arrival and Departure" a novel by Arthur Koestler
"The Act of Creation" A Study of the Conscious and Unconscious in Science and Art by Arthur Koestler
"The Sleepwalker: A History of Man's Changing Vision of the Universe" by Arthur Koestler
"The Age Of Longing" a novel by Arthur Koestler
"The Invisible Writing" Volume 2 Autobiography by Arthur Koestler