Calculus Made Easy by Silvanus P. Thompson and Martin Gardner has long been the most popular calculus primer. 

Introduction to Quantum Mechanics by David J. Griffiths is an introductory textbook on quantum mechanics. 

Visual Group Theory by Nathan Carter approaches the learning of group theory visually.

General Relativity by Robert M. Wald “..lucid, straightforward, mathematically rigorous, exacting in the analysis of the theory in its physical aspect.”—L. P. Hughston

The Princeton Companion to Mathmatics by various authors is a one-of-a-kind reference for anyone with a serious interest in mathematics.

The Feynman Lectures on Physics by Richard Feynman. The legendary introduction to physics from the subject’s greatest teacher.