Polytopes

The Charged Particles Model - Polytopes and optimal packing of p points in n dimensional spheres. Includes a java applet based on a model which allows for generation of multidimensional regular and semi-regular polytopes.
presh.com/hovinga

The Geometry Junkyard - Comprehensive list of links to sites on geometric properties of the shapes.
www.ics.uci.edu/~eppstein/junkyard/polytope.html

Guy's Polyhedra Pages - Vertex figures, filling, faceting diagrams, stellation, defining polytopes through generators, trimethoric and trisynaptic polyhedra, space-filling polyhedra, lost stellations of the icosahedron, and links.
www.queenhill.demon.co.uk/polyhedra/

The Mathematical Atlas - Polytopes and Polyhedra - Collection of discussions regarding volume, vertices, dissection, g-holed tori, and other subjects.
www.math.niu.edu/~rusin/known-math/index/52BXX.html

Numericana - Polyhedra & Polytopes - Enumeration, cartesian coordinates of vertices, naming, and counting the shapes.
home.att.net/~numericana/answer/polyhedra.htm

Pick's Theorem - Describes a theorem for finding an area of simple lattice polygons. Includes proof and Java applet simulation.
www.cut-the-knot.org/ctk/Pick.shtml

Regular Polytopes - Derivation of volume equations for regular polygons, polyhedra, and polytopes, with images.
www.math.rutgers.edu/~erowland/polygons.html

Zome Edu - Educational toys used to teach geometry and model building to create squares, spheres, stars and other regular shapes with sticks and connecting pieces. Products include kits and lesson plans.
www.zometool.com/educators.html