For the mind:
Nonviolent Communication by Marshall Rosenberg - A great book on how to communcate more effectively with others.
Thinking fast and slow by Daniel Kahneman -He is the only psychologist ever to recieve the Nobel Prize if I remember correctly. This book scientifically digests human biases and errors and how they influence our every day lives and decision making. Sometimes it a bit too technical for my taste and I like mostly the first part. (its not an easy read) I rarely had so many Aha-moments.
A random walk down on wall street - For investing your income in stocks. What to do and what no to do. Simple, with facts.
Sapiens by Harari -Interesting, I remember it was a great read and fun read. Connecting a lot of dots :)
On programming:
Designing Data-Intensive Applications by Martin Kleppmann - I am failry a junior web dev, so any material that is clear and explains well is a great source of information and inspiration. This is such a book.
Computer Systems: A Programmer's Perspective by Randal E. Bryant and David R. O'Hallaron - Teaches CS from the basics, which for me is a great source since I don't have a CS degree. I complement it with other materials from the internet (such as Harvard's CS50) for learning the fundamentals paralell working in my daily web dev job. Its a long book, so It will take a couple of months, years to go thorugh, but definitely worth the effort.
Fictions I love, without much introduction: Lord of the Rings Dune (first book) Game of thrones books For me JRRs storytelling is outstanding, the books are better than the serires IMO.
Spiritual Books:
(I am not a religous person by any means and I do not follow traditions) Spirituality for me means a deeper connection with the universe. If I really want to dig deeper than everyday work-life stuff I listen/read these books. Usually when there is a great emotional upheaval in my life or when I feel my daily distractions failed on me.
Power of now by Eckhart Tolle - This book gives me the occasional goosebumps, a great summary of all spiritual teachings (before becoming religions) in a really simple way. If you are interested in such, I highly recommend it.
Meditations by Marcus Aurelius - I see it mentioned here already, no intro needed.
Letters by Seneca - This book is a proof for me that the essential human experience, the core of what makes us human does not change over time. Seneca was a great stoic thinker, who is very relatable by anyone even today (and probably will be for many millenia)
Zen Mind, Beginners Mind by Suzuki Roshi - All true spiritual teaching have the same source, but all are expressed differently. This is a great, simple powerful book to read if you lean towards buddhism.
A Course in Miracles (no official author) -Now this is a heavy read. It has a textbook with daily practices also. This is definitely not a book for everyone.