A good introductory book on cryptography
"Introduction to Modern Cryptography", Jonathan Katz and Yehuda Lindell. This is a great book for learning about provable security.

And for actual crypto protocols and algorithms, there's always the classic: "Handbook of Applied Crypto" by  Paul van Oorschot, A. J. Menezes, and Scott Vanstone. This is more a reference book than a textbook. And its available free of cost on one of the authors web-pages.