Which textbook is good on a given topic depends on the student's current level, and more importantly on what exactly do you want to learn. "Math"?.. A couple of random suggestions that appealed to me aesthetically, but YMMV:

• F. W. Lawvere & S. H. Schanuel (1991). Conceptual mathematics: a first introduction to categories. Buffalo Workshop Press, Buffalo, NY, USA.
• S. Mac Lane & G. Birkhoff (1999). Algebra. American Mathematical Society, 3 edn.

(Both can be found on Kad.)