Wolfram Research
Wolfram Math World: Platonic Solids
This site, which is provided for by Math World, is a lengthy site describing the various properties and mathematical explanations of the figures.
Clark University
Clark University: Euclid's Elements
A review of the 13 books of Euclid's "Elements" text can be found here. Each of the chapters are broken down into definitions, propositions, and common notations that are used throughout this overview.