Books and Articles:
Naomi Pacachoff, Marie Curie and the Science of Radioactivity, Oxford University Press, 1997.
Bjorn Walhstrom, Understanding Radiation, Medical Physics Pub. Corp., 1996.
The ABCs of Radioactivity A series of experiments on the basic properties of radioactivity. This site was developed by the creators of the Nuclear Science Wall Chart.
The Discovery of Radioactivity: The Dawn of the Nuclear Age A description of the key experiments leading to the discovery and characterization of radioactivity and the people who did them. Developed by Genentech.
Table of Nuclides An online table of the nuclides giving information such as branching ratios and half-lives for any isotope.