Links

The textbook, "Introduction to Probability" by Grinstead and Snell, is available online. Particularly interesting resources available on this page include:

Java versions of the programs referenced in the text.

Versions of the programs in other languages are also available.

Answers to odd-numbered problems.
Of course, the book itself (in PDF format).

Wikipedia is, perhaps surprisingly, not a bad source for background material on basic definitions and results in many areas of mathematics, including probability.