Scientific experiementation at the amateur level — experiments that you can (and should) try at home.
MadSci Network, 36,000+ answerwed science questions, plus FAQs, library files, experiments and more.
Mad Science is about exploring and manipulating aspects of the natural world without the facilities or resources of “sane science” as practiced in academic, industrial, and governmental research settings
DIY projects and ideas at House Hacker.
The Sciencemadness library: 40,000+ pages, 90+ volumes
Theodore Gray’s Popular Science columns