Wolfram Research
Wolfram Math World: Multiple Angle Formulas
A site from Mathworld on multiple angle formulas. This site shows how to express sin(nx)in terms of sin(x) and cos(x) using the binomial theorem and Euler's formula. If you are not yet familiar with these formulas, check out the links to...
Other
Technical Tutoring: Trigonometry: The Very Fast Review
This site is a quick review of the functions and identities in trigonometry. Very helpful site.
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.