I only read non-fiction; mostly philosophy. Here are some books off the top of my head:
* The Inner Citadel/Philosophy as a Way of Life by Pierre Hadot
* Plato's dialogues (someone already mentioned a few of them, but the Republic was missing from their list).
* Epictetus (Discourses and Enchiridion)
* The various essays/letters of Seneca
* Matter and Consciousness by Churchland (older, but fascinating)
* The Mediations of Marcus Aurelius
* (mostly) any Buddhist texts
* What a Plant Knows
* Moonwalking with Einstein
There are tons of fascinating books, way too many to list.