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.
http://presh.com/hovinga

The Geometry Junkyard
Comprehensive list of links to sites on geometric properties of the shapes.
http://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.
http://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.
http://www.math.niu.edu/~rusin/known-math/index/52BXX.html

Numericana - Polyhedra & Polytopes
Enumeration, cartesian coordinates of vertices, naming, and counting the shapes.
http://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.
http://www.cut-the-knot.org/ctk/Pick.shtml

Regular Polytopes
Derivation of volume equations for regular polygons, polyhedra, and polytopes, with images.
http://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.
http://www.zometool.com/educators.html