Interactive Mathematics
Interactive Mathematics: Trigonometric Functions
This is a excellent review lesson about trigonometric functions of any angle. Good examples here.
Other
Brown Math: Remembering Trig Identities
Faced with a large number of trigonometric identities, students tend to try to memorize them all. This site the emphasis is on understanding how the functions work and on memorizing only about a half dozen of them - all the others work...
Wolfram Research
Wolfram Math World: Hyperbolic Functions
This site from MathWorld explains the hyperbolic function. The information is not too in-depth, but factual and quite a few links are provided for additional information on related subjects.
Math Open Reference
Math Open Reference: Trigonometry Functions Introduction
A complete reference guide to trigonometry functions. It provides definitions, examples, and an interactive activity that enhances further explanation. Includes links to related topics.