The Chaos Hypertextbook by Glenn Elert is the best web page I’ve found on Chaos.
David Wright’s Dynamical Systems and Fractals Lecture Notes are fairly mathematical and only marginally related to Chaos, but we’ll be working with things from these notes later.
Introduction to Chaos has a lot of Java applets to investigate chaotic behavior.
Somebody else’s collection of chaos and nonlinear dynamics links.
Yahoo’s chaos links.