Tiny Bison

Science Toys is an incredible site for kids and adults alike. It covers a wide array of fun, science-oriented toys to build. From the site:

Make toys at home with common household materials, often in only a few minutes, that demonstrate fascinating scientific principles. To make it easier to build some of the toys described in the book we have a catalog of parts and kits.

The site spans a wide array of topics, including magnetism, electromagnetism, electrochemistry, radio, thermodynamics, aerodynamics, light and optics, biology, mathematics, and computers and electronics. Projects range from an AM transmitters to hydrogen fuel cells, from a solar hotdog cooker to a 10 minute railgun. Fun fun fun.