American Association of Physics Teachers
Com Padre Digital Library: Open Source Physics: Electric Field and Potential
An electrostatic simulation that moves beyond the two-dimensional representations a book may provide. Try this Gauss' Law model which shows the electric field and potential for cylindrical and spherical symmetry.
Other
Symmetry in Architecture
Provides real world examples of symmetry in architecture, including pictures of each kind of symmetry, examples, acknowledgements, and a bibliography.