All the books below have shaped my thought process to a significant degree. I started reading late but I'm fortunate enough to have stumbled upon these gems.
"Debt: The First 5000 Years": This is truly a magnum opus. Until I read this I had taken money, economy, market etc., for granted. And I had held onto the widely accepted, but naive, view that economic systems somehow grew out of barter systems. The range of topics discussed, and the way author shows how seemingly independent concepts are intertwined, is truly astonishing. I'm on my 2nd read.
"Thinking, Fast and Slow": This book made me truly appreciate the value of psychology. I didn't even know the existence of a vast domain called behavioral science until I read this book. Now I'm deliberately conscious about the decisions I take and retrace my thought process multiple times just to make sure that I haven't fallen pray to some of the cognitive biases.
"The Tell-Tale Brain": While I did know that human brain is a unique organ this book opened my eyes to its layered complexities. For instance, how "seeing" is not a single step but a multi step process. From image formation, to identifying the object, to evoking emotional response.
"QED: The Strange Theory of Light and Matter": The book with the highest signal to noise ratio. I finally understood what science is about, a way to model nature and to keep refining it to fit the observation. There are no true/false theories/models only those that explain nature's behavior better or worse. Nature is agnostic to all our theories and models. She's just the way she is. For details read about double slit experiment.
"How the World Works": This one along with "Profit Over People: Neoliberalism & Global Order" has greatly shaped my mental model about the workings of contemporary world. I now understand why does military gets all the funding, why do powerful governments tend to keep its subject under perpetual fear, why is it that the cost of education has been sky-rocketing.
"The Hanging of Afzal Guru and the Strange Case of the Attack on the Indian Parliament": A glimpse into the working of Indian justice system.
"Broken Republic": This is by far the most accurate description about current affairs in India. How India is being hollowed out and how its most vulnerable section is the one fighting against it.
"Grammatical Man: Information, Entropy, Language and Life": I'm currently reading it (20% through) and it has already made a big impact. The meaning of information is deep and subtle and pervades not just human being but the life itself.
"The Order of Time": The book that well and truly shook the foundation that I had taken for granted for my entire life. That space and time aren't something absolute and are personal has had a profound impact on me.
"The Upanisads": A truly remarkable work of human mind. Just to think about some of the concepts uplifts my mood.