The EPA's "A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon"
The National Safety Council addresses Radon, offers testing kits, and outreach materials. [pdf file]
The NSC list of Frequently Asked Questions about Radon (with answers). [.doc file]
The SD DENR maintains this information page about Radon concerns in South Dakota.
The National Environmental Health Association's "National Radon Proficiency Program" - be sure to check the "Checklist for Consumers"
The American Association of Radon Scientists and Technologists publishes this online guide to "Radon Risks and Health Effects"
Lung Cancer: It's Not Just From Smoking! (their slogan says it all)