Higher Dimensional

Four-Space Visualization of 4D Objects
Mathematical and computer programming oriented approach. Discusses wireframe rendering and ray-tracing.
http://stevehollasch.com/thesis/

Fourth Dimension: Tetraspace
A discussion of rotation, levitation, wheels, and bodies of water. Classification of "rotatopes" (cubes, spheres, and cylinders), and a Java applet to visualize projections and intersections of the shapes. Includes book reviews, a glossary, links, and a forum.
http://tetraspace.alkaline.org

Hyper Dimensia
Tutorial which aims to give readers an understanding of the fourth dimension by having them use a java applet to rotate a cube and a hypercube to see multiple views of the shapes at once.
http://www.hyperdimensia.com/

HyperCube by Harmen
A short introduction to the fourth dimension, plus a hypercube java applet game.
http://www1.tip.nl/~t515027/hypercube.html

Hypercube's homepage
Philosophy, math, and cosmology related to the fourth dimension.
http://www.geocities.com/CapeCanaveral/7997/

Hyperspace Structures - Exploring the Fourth Dimension
Introduction to the hypercube, hyper-torus, and approximation to the hypersphere. Page includes mpeg movie clips to illustration the various objects.
http://www.lboro.ac.uk/departments/ma/gallery/hyper/

Hyperspace Travel
Images and animations of a couple of four-dimensional objects, along with the math and source code used to produce them. Links to software to interactively visualize four-dimensional objects.
http://www.hyperspace-travel.de

Miscellaneous Mathematical Musings
Introduction to dimensions, multi-dimensional geometric units, and formulas for calculating higher-dimensional phenomena.
http://www.geocities.com/bprice1949/math.html

Thinking 4-d
Focuses on helping the reader to conceive of the fourth spatial dimension, and in particular discusses hypercubes and hyperspheres.
http://www.geocities.com/jsfhome/Think4d/think4d.html