Other
Dans Math: Lessons: Calculus (Part 2)
College professor Dan Bach offers a review of the calculus concepts of integrals and vectors. Examples and animated graphs are provided.
Windstream
Ojk's Precalculus Study Page: Functions of Two Variables
An introduction to functions with two variables, including several examples relating to linear programming. The tutorial includes graphical examples of the functions and also review questions located at the bottom of the page.