PBS
Nova Online: The Diamond Deception
A good overview of diamonds. Gives information on structure, properties, and origin. Includes models that can be rotated and examined in 3D. Also has activity for building your own carbon atom.
New York University
Mathmol Home Page: The Chemistry of Carbon
The basic properties of three allotropes of carbon are presented as downloadable models.
Other
Math and Science Activity Center: The Element Carbon
Allotropes of carbon are described, and 3D models that can be manipulated are included for diamond, carbon, and fullerenes.
Other
Chemistry 1341 Lecture Notes: Inorganic Carbon Compounds
The forms of inorganic carbon are discussed in terms of their hybridization, stability, reactivity, and uses.
Florida-Spectrum Environmental Services
Florida Spectrum: Chemical Fact Sheet: Carbon
Summary of the uses, history, properties, proper disposal, and environmental fate of the various forms of carbon. The various allotropes of carbon are described in detail.