Last summer, I read Euclid's Elements, and it was an eye-opening experience; I had assumed that three thousand years' difference would make the notation incomprehensible and the reasoning alien, but his proofs were beautiful; I had never experienced synthetic geometry (at least since middle school), and it was very enjoyable, especially his 3-dimensional geometry and the classification of platonic solids.

The experience made me realize that older math books could be worthwhile to study; for instance, I've heard that Euler wrote some incredibly popular calculus books, and that others (like Maclaurin and L'Hopital) wrote popular textbooks.

What math books from before 1900 (or from the beginnings of newer areas like topology and category theory) have you read and enjoyed? Are there any you would recommend?

mucholder math texts, especially those from outside the Eurocentric canon. You could start with Katz's book as a source for excerpts, and look up full books when interested. – Marty Apr 19 '13 at 13:12