David J. Morin is a physics instructor at Harvard who has published several books based on his classes. They have good reviews on Amazon. Maybe others could add recent math/science books for undergrads (which could be accessible for gifted students before college). Comparable threads for the social sciences and humanities could also be created.

The Green-Eyed Dragons and Other Mathematical Monsters (2018)
Special Relativity: For the Enthusiastic Beginner (2017)
Probability: For the Enthusiastic Beginner (2016)
Problems and Solutions in Introductory Mechanics (2014)
Electricity and Magnetism (2013) (revision of Purcell)
Introduction to Classical Mechanics: With Problems and Solutions (2008)