Interactive Mathematics
Interactive Mathematics: Trigonometric Functions
This is a excellent review lesson about trigonometric functions of any angle. Good examples here.
Iowa State University
Inverse Trigonometric Functions
This trigonometry tutorial features an explanation of how the inverse of all six of the trigonometric functions are obtained--and includes a Java applet for further reinforcement of the concept.
Calculator Soup
Calculator Soup: Trigonometric Functions Calculator
This online trigonometry calculator will calculate the sine, cosine, tangent, cotangent, secant and cosecant of angle values entered in degrees or radians. The trigonometric functions are also known as the circular functions.
eFunda
E Funda: Multiple Angle
At this site from eFunda you can scroll to the middle of the page for a listing of multiple angle formulas for cos, sin, and tan.