A nice introduction into nonlinear dynamics with many Java applets.
Textbooks
R.H. Abraham and C.D. Shaw:Dynamics: The Geometry of Behavior,
(4 volumes), Aerial Press, 1982-88.
Beautiful picture books.
G.L. Baker and J.G. Gollub:Chaotic dynamics -- an introduction,
Cambridge University Press, 1990, (2.ed) 1996.
An elementary introduction where the pendulum driven by a periodic force
is the central thread. With listings of computer programs.
P. Bergé, Y. Pomeau und Ch. Vidal:Order within chaos -- Towards
a deterministic approach to turbulence, John Wiley \& Sons, New York, und
Hermann, Paris, 1986.
A classical introduction into nonlinear dynamics from the viewpoint of physics.
J. Guckenheimer and Ph. Holmes:Nonlinear Oscillations, Dynamical
Systems, and Bifurcations of Vector Fields, Springer-Verlag, 1983.
A classical and readable textbook about the mathematical aspects
of nonlinear dynamics.