Links

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/

Reference Topics

Here is a good site for graphing equations of the form "y =".
It is easy to use, but does not graph exponentials.
http://www.webgraphing.com/graphing_basic.jsp

This is a general site for graphing lines, parabolas, and exponentials.
http://www.digitalhermit.com/math/calc/