Discovery Education
Discovery Education: Web Math: Try to Simplify a Trigonometric Expression
This WebMath site is a java program that will simplify a trig expression. This is a good site to use to check answers to problem sets. Read the site instructions carefully.
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.