In no particular order
1. Nietzsche-Beyond Good and Evil
2. Charles Darwin- The Origin of the Species
3. Karl Marx- Das Kapital
4. Richard Wagner- the Ring Cycle
5. James Frazer- The Golden Bough
6. Leo Tolstoy- War and Peace
7. Sigmund Freud- The Interpretation of Dreams
8. Marcel Proust- Remembrance of Things Past
Many of these can be seen as repudiations on religion, on that inherent natural order of God and subjects. Many of these are direct descendants of the Enlightenment and Democracy, natural extensions of I am free, I am Man, I am the Master of my own Fate, I make my own Moral universe, type of reasoning.
It is also notable that this apparent devaluation of religion was coupled with a great enhancement in the attraction of nationalism, in the understanding that nations were at the heart of identity. Religion wanes (not really, but for the purposes of this discussion) and so nationalism strengthens. People need to identify with something is my simplistic conclusion. Hence, the inclusion of Wagner in this list; Wagner stokes the flames of German nationalism. Remember, Germany was not even a country until the 1870s, just a collection of individual states (Bohemia, Saxony, etc…) not unlike Italy at the time. Nietzsche and Wagner were contemporaries; God is dead, Nation is king. Once again, rather simplistic.
An interesting parallel to this was the seemingly contradictory notion that missionary movements were at their zenith in places like Africa and Asia, and not coincidentally, so was European colonialism. Unfortunately, the two seem to go hand in hand for stretches of human history.