Useful links

The following links are quite good:

   http://www.vashti.net/mceinc/golden.htm

   http://www.jimloy.com/geometry/goldenz.htm

A more formal definition can be found at

   http://mathworld.wolfram.com/GoldenRectangle/html

And there is quite a nice animation of the golden rectangle and spiral at

   http://library.thinkquest.org/27890/goldenRatio1a.html

Further reading

Introduction to Geometry, Coxeter, H.S.M. (John Wiley, 1969)

The Divine Proportion, Hartley, H.E. (Dover, 1970)

The Golden Section, Runion, G.E. (Scott Foresman, 1972)