I had a page on my Notre Dame website called mathlinks. This isn’t the same collection but it falls into the same category.

• The math genealogy page is always interesting reading.
• A translation of Euclid’s Elements by Richard Fitzpatrick.
• The University of Michigan’s Historical Mathematics Collection.
• A page of famous codes and ciphers.
• Animated GIF that I like for no good reason
• An excellent site to point students to is Understanding Mathematics by Peter Alfeld at the University of Utah.
• For review of high school skills assumed by the text (such as polynomial long division), I have pointed my students to S.O.S. Math, which has an easy to navigate layout and explanations plus exercises with answers.
• The Quine Page: self-reproducing code. Not updated in a long time but features a lot of examples
• Fooplot online graphing calculator; allows export of graph as svg, eps, pdf, or png
• Another online graphing calculator
• Java Graphers, applet graphing calculators that include 3D capability