Robert Pirsig, Zen and the Art of Motorcycle Maintenance — possibly one of the best introductions to philosophy, especially philosophy of science. It also introduces Pirsig's innovative concept of the metaphysics of quality that arise from his noticing that there exists something third other than the subjective perception and objective reality. Good jumping-off point to some more ancient philosophy like Aristotle and Plato. Some of my Discovery character stories borrow liberally from it. It's also got a great story.
Paul Feyerabend, Against Method — again one of the best books on philosophy of science, showing the flaws in the understanding of the system of scientific progress. Very good at dispelling the myth of validity of pseudoscientific fields such as psychology or economics.
Nassim Nicholas Taleb, Antifragile — possibly one of the best of Taleb's books that's been bastardized and misunderstood by pretty much everyone I've ever met. I do not think that I fully understand what he's saying either, but the core concept of looking for things that improve under uncertainty is a fantastic life lesson.
Ibn Tufail, Hayy ibn Yaqzan — a proof of how one can reach spiritual truths by observing the material world
Theology
The Bible obviously
Rule of Saint Benedict alongside all manner of supporting material — my main object of private study for the last four years, one of the pillars of Western civilization, possibly one of the greatest books in history.
C. S. Lewis, Mere Christianity — good summary of the Christian faith
Augustine, Confessions — the autobiography of one of the greatest minds of Christianity, a great source for practical application of Christian morals, neoplatonist philosophy, and scriptural exegesis on Genesis (only F.J. Sheed's English translation is good)
G. K. Chesterton, Orthodoxy — a good-natured essay by one of the most profound writers of the modern era
History
Fustel de Coulanges, The Ancient City — definitely one of the better books on the ancient history of Europe, dispelling all manner of myths and misconceptions about the Romans and Greeks. Many analogues to present day.
Anna Komnene, Alexiad — the biography of Byzantine emperor Alexios I Komnenos written by his daughter, exceptional read, beautifully written.
Nicholson Baker, Human Smoke — a story of the lead up to and the first two years of World War II, written by means of tweet-long, newspaper-like vignettes from a variety of perspectives, with copious source references.
Politics
Plato, Republic — basically why materialism in government doesn't work.
Joseph de Maistre, Essay on the Generative Principle of Political Constitutions — basically why rule of law doesn't work.
Gustave le Bon, Psychology of Crowds — basically why large groups of people don't work.
Science
Stephen Schanuel, William Lawvere, Conceptual Mathematics — the best textbook on category theory I managed to find.
Charles Petzold, Code — a great introduction to the technology behind computers.
Fiction
Zero HP Lovecraft, They Had No Deepness Of Earth — not to be confused with H. P. Lovecraft, this is a fantastic collection of technological horror stories. The book is available somewhere to download as a free pdf. It's notable for being possibly the first book to be released as crypto NFTs that could be exchanged for physical copies. The best story imo from it is available here.
Jacek Dukaj, Inne pieśni — possibly the most impressive worldbuilding since LotR, I'm so sorry you can't read it if you don't know Polish.
Walter M. Miller, Jr., A Canticle for Leibowitz — a post-apocalyptic social science novel set in a Catholic monastery in North America after a nuclear war wiped most of humanity and reduced the civilizational progress back to stone age, follows the story of monks who preserved scientific knowledge. Lots of discussions about separation of church and state and overall morality of a society.
Alexandre Dumas, The Count of Monte Cristo — a classic high adventure novel, amazing for a light read.
Interestingly the myths in these two books are extremely similar. Like, for example, the passage where Indra defeats Vritra reminds me of Susanoo defeating Yamata-no-Orochi, which may be useful for comparing seemingly unrelated things and proving a common origin to these.
The Golem by Gustav Meyrink – the book that introduced me to occult, written by a man who closely studied theosophy and Kabbalah among other topics
The Company Man by Robert Jackson Bennett – a supernatural detective story in a grim dieselpunk setting
Mark Hodder's Burton and Swinburne cycle – even more meshing of supernatural, occult and bizarre scientific breakthroughs with historical personages as main and supportive characters (from Burke and Hare to Isambard Kingdom Brunel to Helena Blavatsky)
H. P. Lovecraft, the entirety of his works
Nikolai Gogol's The Government Inspector and Dead Souls
Mikhail Bulgakov's The Master and Margarita
Ray Bradbury's Something Wicked This Way Comes
Harry Harrison's Stainless Steel Rat, Deathworld and Bill the Galactic Hero
Edgar Rice Burroughs's John Carter of Mars
My favourite authors are Andy McNab, Mark Greaney and Louis L'Amour.
Of McNab's novels, Meltdown(first one I read) is my favourite, as well as the entire Nick Stone series. I don't quite enjoy the newer Tom Buckingham series as much as the Nick Stone series but it is still good.
Of Greaney's books, Gray Man has been my absolute favourite. Can't describe how much I enjoyed it in audio book form. Too bad the movie sucked.
Of L'Amour's books, Conagher is my all time favourite, and the Wyatt Earp books are really good reads as well.
As for poems, I haven't really seen many, so my sample size is tiny. My dad wrote poems, and one of his poems that he wrote for my mom is incredibly beautiful. It's in Afrikaans and I can't properly translate it to have the same meaning as he wanted it to have(not that it can't be done, I just don't know how). Please forgive me for not translating