I’ll go first:
Calculus and Analytic Geometry (1951) by George Thomas
It’s readily available for < $10 and I find it’s style much more engaging than contemporary textbooks on the same topic.
And a bonus one - when we had questions for the doctor when my wife was pregnant, I read the beginning of this and can say with reasonably certainty that I reduced the probably of some negative outcomes as a result:
Callen's Ultrasonography in Obstetrics and Gynecology (Mary Norton, 2016)
"Starting Forth" - Leo Brodie
"Computer Science, Logo-Style" series - Brian Harvey
"Algebra", "Functions and Graphs", "Methods of Coordinates", "Trigonometry" - I.M. Gelfand (does anyone know if he completed his Geometry textbook? I've never seen it. I've also never seen his "Calculus" or "Combinatorics" books, although I know they exist. I suspect his "Combinatorics" book is more advanced than he intended to produce.)
"Sage for Undergraduates" - Gregory Bard
A brilliant epic journey through the history of what we'd now call physics, beginning from primitive man pondering the night sky, right through to splitting the atom and the atomic age. Written for the non-scientist in such a way that the reader's understanding of the subject evolves with the book's journey through the centuries.
Sadly out of print now, it seems and I lent someone my copy and never got it back.