Anything by Aleksandr Solzhenitsyn is thought provoking. For those unfamiliar he was imprisoned in Stalin's GULAG Labor camp system for a decade after WW2 and wrote of the inhuman conditions in the camps and utter madness of the USSR police state. Many have disagreed with some of his political conclusions, but it would be hard to argue that the man did not have a profound handle on suffering, what's important in life and the human condition. Some titles if anyone's interested: One Day In The Life of Ivan Denisovich- semi-autobiographical stream of consciousness account of one prisoner's day in the camp. Cancer Ward- studies a group of Soviet citizens from all walks of life in Stalin's USSR undergoing treatment for various forms of cancer, the ward is a microcosm for Soviet society. this may be Solzhenitsyn's most profound work.
The GULAG Archipelago- Solzhenitsyn's master work, his own story of arrest, imprisonment and release combined with the input of over 200 other prisoners paints a complete picture of the breadth of oppression rampant in the USSR during those years. It is a massive work including his story, the stories of others and many essays and asides about various aspects of the camps and the system which made them possible. All amazing reads .
If you like Day in the Life, you should definitely give Cancer Ward a shot. Having read Day in the Life you will definitely understand whats going on with it's main character and appreciate it that much more.