Exploratorium
Exploratorium: Science Explorer: An Exploratorium at Home Book
Over 30 simple, interactive, experiments can be found on the Exploratorium site. This museum, based out of San Francisco, presents each experiment with a list of materials, a short procedure, and the scientific reasoning behind the...
Other
Science at Home: The World of Matter
Science at Home offers this site full of simple experiments that can be conducted at home. Don't miss the other sections, "forces and energy" and "electrons in action".
US Department of Education
U.s. Department of Education: Science in the Home Activities
You don't need to be a science teacher in order to teach science at home! This site has a great list of activities along with everything you will need to conduct them.