Franklin Institute Online
This site features each of the 6 machines with good descriptions of the machines. Follow the extra information links for some cool Lego projects.

Think Quest Simple Machines
This site was created by students. It includes simple descriptions and photographs of samples of each of the simple machines.

Marvleous Machines
This is a series of experiments about simple machines: levers, wheels and inclined planes. This unit was designed for use in the third grade, but certainly can be adapted.

Inventor's ToolBox
Information and pictures of more than the basic six. It has a link to an Identifcation activity.