Mathlets (mathematics applet animations)

EDinfomatics Interactive Library - Mathematics - Incredible listing of animations

Manipula Math Applet Collection (from IES) - VERY nice, simple, and clean applets covering:

Introductory math (Walter Fendt at Paul-Klee-Gymnasium, Germany)
Sophisticated power, but clear and simple - in English!

BrainTrax (Missouri University of Science and Technology) - Paced tutorials to help increase student success (particularly struggling students) in algebra, geometry, and calculus.

Graphing applets (from the Java Project) - three educational applets for graphing