A doorway to a HUGE amount of fractal information. Images... programs... etc.
http://spanky.triumf.ca/www/welcome1.html
Perfect for high school, Bob Devaney's site at Boston University is a 'must visit'!
http://math.bu.edu/DYSYS/dysys.html
Society for Chaos Theory in Psychology and Life Sciences
http://www.societyforchaostheory.org
Actually, what the heck am I doing trying to put links here.
Just google 'fractals' or 'mandelbrot set' or 'chaos theory'. Nobody does it better...
...come to think of it, here's a link to a tutorial that will help you get Fractal Explorer going...
http://www.fractalfairy.com/fe_tutorial/