Software

Stella: Polyhedron Navigator - A program for creating, visualising, and printing nets for 3D polyhedra and 4D polytopes.
http://www.software3d.com/Stella.php

PEEK - A program to interactively explore arbitrary dimension polytopes through the use of cross-sections and projections.
http://www.cs.utah.edu/~gk/peek/peek.html

PPL: The Parma Polyhedra Library - A C++ library for the manipulation of convex polyhedra. Distributed under the terms of the GNU General Public License.
http://www.cs.unipr.it/ppl/

Polyhedra by Bob - Images and software. Poly is a free DOS program that can be used to study the truncations and transformations of the Platonic Solids.
http://members.ozemail.com.au/~llan/polhed.html

POLY - Shareware Macintosh/Windows software for exploring and constructing polyhedra. Flattened versions (nets) of polyhedra may be printed and then cut out, folded, and taped, to produce three-dimensional models.
http://www.peda.com/poly/

Polyhedra 2001 - OpenGL program which displays the uniform polyhedra and related shapes in real time. The shapes may be morphed in to their duals, exploded, truncated and unfolded into a net. Free download.
http://gratrix.net/polyhedra/2001/

The Many Faces of Polyhedrons - A Windows program in which you can interactively manipulate regular and semiregular polyhedra.
http://home.twcny.rr.com/fisheryorks/mfop/mfop.html

Hypercube Downloads by Rudy Rucker and Farideh Dormishian - A shareware program for Windows called Hypercube 98 that shows tumbling four-dimensional hypercubes as well as some 3D polyhedra and some 2d snowflakes.
http://www.mathcs.sjsu.edu/faculty/rucker/hypercube.htm