Comment by 0xmattf
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.
Second the recommendation for "Moonwalking with Einstein." Ed Cooke (the memory coach and world memory champion featured prominently in the book) is also a really nice chap.
If you have any interest in memorization or mnemonics, it's a great read.