Clark University
Clark University: Dave's Short Trig Course: Trigonometric Functions
The Clark University site shows and explains the graphs of the six trigonometric functions. It explains how to find an arbitrary angle measurement using trig. Also, it explains that sine and cosine functions are complementary.
Interactive Mathematics
Interactive Mathematics: Graphs of Tangent, Cotangent, Secant, and Cosecant
The tutorial explores the graphs of the tangent, cotangent, secant, and cosecant functions. The resource consists of animations and examples.
Wolfram Research
Wolfram Math World: Cotangent
Graphs of the cotangent function, both 2-dimensional and 3-dimensional. Higher level mathematics applications given including the Macluarin series.
Interactive Mathematics
Interactive Mathematics: Trigonometric Functions
Just about everything you need to know about trigonometry can be found here. Interactive examples and demonstrations help to enhance the lessons. Although not required, the tutorial uses Live Math and Scientific Notebook.