This Applet Lets the student visualize the connection
between lengths of a figure connected from the unit circle and the
standard trig functions of an angle.

The point P can be dragged around the unit circle.
The values of the 6 standard trig functions are given and the sin and cos curve are traced out.

GeoGebra is a GNUed software package for mathematics visualization.
The home for the applications is http://www.geogebra.org.