The following demonstrations from the Wolfram Demonstrations Project.  These particular demonstrations are to help you in your understanding of the sine and cosine functions and their relationship to the unit circle.  In order to view the demonstrations, you need to have Mathematica Player on your computer.  Mathematica Player is a free download. 

Illustrating Sine with the Unit Circle

http://demonstrations.wolfram.com/IllustratingSineWithTheUnitCircle/

Illustrating Cosine with the Unit Circle

http://demonstrations.wolfram.com/IllustratingCosineWithTheUnitCircle/

Relationship of Sine and Cosine to the Unit Circle

http://demonstrations.wolfram.com/RelationshipOfSineAndCosineToTheUnitCircle/

Sine and Cosine Function Game

http://demonstrations.wolfram.com/SinCosFunctionGame/