University of Colorado
University of Colorado: Ph Et Interactive Simulations: Conductivity
Experiment with conductivity in metals, plastics and photoconductors. See why metals conduct and plastics don't, and why some materials conduct only when you shine a flashlight on them. Java required.
Simon Fraser University
Chem1 Virtual Textbook: Metals, Insulators and Semiconductors
Acting as an overview from the General Chemistry Virtual Textbook, this site explores insulators in relation to metals and other semiconductors. Other topics include conduction band, dielectric breakdown, photoconductors, and more.