Links

Videos

The Cartesian Plane - this is an excellent introduction  (time: 3:11)
http://www.youtube.com/watch?v=9EpfpFexoNQ

Graph a line by plotting points (time: 7:59)
http://www.youtube.com/watch?v=07z_75PgjPg

Graph a line using the slope and intercept (time: 7:16)
http://www.youtube.com/watch?v=x-g4c9UDZQQ

History

This is one of the best all around sites that I have found. It is titled "The MacTutor History of Mathematics Archive."
http://www-history.mcs.st-and.ac.uk/~history/

This is an award-winning site that links to all sorts of mathematics information.
http://archives.math.utk.edu/

Descartes:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Descartes.html

Reference Topics

Here is a good site for graphing lines.
http://www.webmath.com/gline.html

You can use this site to graph several lines at the same time.
http://cs.jsu.edu/mcis/faculty/leathrum/Mathlets/grapher.html