Introductory

• Geometry Center Viewing Four-dimensional Objects In Three Dimensions and guided demonstration with animations
• Davide Cervone's introduction to the fourth dimension at his and Thomas Banchoff's Beyond 3D
• Jurgen Koller's hypercube intro
• Alex Bogomolny's interactive Tesseract intro with Java applets

Java Applets

• Mark Newbold's Stereoscopic Animated Hypercube. Check out his other Java stuff too.
• Michael Gibbs' 4D Polytope Viewer shows 15 different 4-d polytopes
• Richard Koch's viewer shows all the regular 3-d and 4-d polytopes

Polytopes and Polyhedra

• Eric Swab's Visualization of Space
• George Olshevsky's Uniform Polytopes in Four Dimensions
• George Hart's Encyclopedia of Polyhedra

Links Pages

• Mike D'Zmura's 4D Web Page
• Garrett Jones' links at his Fourth Dimension: Tetraspace
• Google Directory
• Yahoo Directory

Miscellanea

• Jonathan Bowen's Hypercube Images