University of Pennsylvania
University of Pennsylvania: Solid State Chemistry: Describing Crystalline Solids
This site contains in-depth information on crystalline solids. Includes basic concepts, pictures, learning graphs, and useful tools.
Wikimedia
Wikipedia: Amorphous Solid
This page from the Wikipedia encyclopedia on amorphous solids contains information on examples of, the difference between amorphous solids and crystalline solid, and the transition between a very viscous liquid and an amorphous solid.