These are pretty cool. I don't know what direction would be best to take these in. Maybe you just choose things you want to learn about or thought were hard to understand? I like the gamification of the vector applet, so maybe you could explore that with simple concepts?
"An algorithm for turning polygon in triangles" why did the paradox get an explanation and not the algorithm? :(
With regards to your sorting applet, I don't like that you can rearrange bars other than the one you are dragging. Having the index above the bar is confusing to me. I would expect a number above the bar to be its height, not its index. I think a visualization of various sorting algorithms that plays an animation that steps through pseudo-code is more useful than a scripting language.
Newton's method, space filling curves, bezier curves, trig functions
math / physics bits: http://www.euclideanspace.com/
You could make some sort of quaternion visualizer like this
Some algorithm / data structure visualizations are available here