These are some of the non-textbooks which I've enjoyed reading. Maybe there are a few ideas for your own reading list.

- How to Solve It
- Mathematics and Plausible Reasoning
- Pilgrim’s Progress
- Man’s Search for Meaning
- The Lord of the Rings
- The Federalist Papers
- The 7 Habits of Highly Effective People
- Around the World in 80 Days
- The Courage to Be Disliked
- The Upside of Stress
- Medieval Technology and Social Change
- The Road Less Traveled
- The Inner Game of Tennis
- The Sovereign Individual
- Flow
- Mindset
- The Narrow Road to the Deep North and Other Travel Sketches
- The American Technological Challenge
- The Analects
- The Art of Doing Science and Engineering
- The Dip

- Foundations of Modern Probability (O. Kallenberg)
- Random Measures: Theory and Applications (O. Kallenberg)
- Probability: Theory and Examples (R. Durrett)
- An Introduction to Measure Theory (T. Tao)
- Analysis I & II (T. Tao)
- Complex Analysis (E. Stein and R. Shakarchi)
- Modern Real Analysis (W.P. Ziemer)
- Algebra (T.W. Hungerford)
- Topology (J. Munkres)
- Set Theory (T. Jech)
- Partial Differential Equations (L.C. Evans)
- Convex Analysis (R.T. Rockafellar)
- Convex Optimization (S. Boyd and L. Vandenberghe)
- The Probabilistic Method (N. Alon and J.H. Spencer)
- Introduction to the Theory of Computation (M. Sipser)
- Elements of Information Theory (T.M. Cover and J.A. Thomas)