Math 135A Textbook Information

Official Textbook of Course: Probability and Random Processes, third edition, by G. Grimmett and D. Stirzaker
See also the companion book One Thousand Exercises in Probability.

A free book -- more elementary than the course material but insightful:
Introduction to Probability, Second revised edition, by Charles M. Grinstead and J. Laurie Snell.
Additional information can be found at the Chance website.