In MatematicasVisuales we try to see mathematical concepts. If you want to learn more about the ideas involved you can find useful information in
It is a very big site about mathematics with visualization applications made using Mathematica.
More Java applets:
Applets Java of Mathematics Walter Fendt
Math Education and Technology - IES International Education Software
Complex functions:
Tristan Needham - Visual Complex Analysis.
A wonderful book.
Frank Farris - Visualizing complex-valued functions in the plane
Farris introduces a new way to use color in visualizing complex-valued functions in the plane.
He has a very famous video about Moebius functions.
Flash and ActionScript programming
Barbara Kaskosz and Doug Ensley develop a site about Mathematics and Flash with lots of examples and
good advice to program in Flash. You need to know this site if you want lo learn how to develop mathlets in Flash.