Wolfram Research
Wolfram Math World: Spherical Coordinates
This site provides a general overview of spherical coordinates, the system of curvilinear coordinates which describes positions on a sphere or spheroid.
National Council of Teachers of Mathematics
The Math Forum: Ellipsoid, Torus, Spherical Polygon Formulas
Curious as to what an ellipsoid is? Dr. Math provides a picture and a brief description. This site also has information pertaining to a torus, and spherical polygon.