USA Gov for Science
http://www.science.gov/index.html Index to various government documents and databases in the sciences. Authoritative and free!
BBC Science and Nature Visuals
http://www.bbc.co.uk/science/humanbody/body/index_interactivebody.shtml Lots of interactive visuals of the body. Much of this is also useful for psychology and human behavior.
http://www.sciencedaily.com Offers a collection of links to the most recent science, technology and medical research results from leading universities and organizations around the world.
http://medlineplus.gov/ Authoritative and comprehensive health topics.
National Science Digital Library
http://nsdl.org/ Searchable by topic, age level, type of file. Includes research, lessons, interactive materials, video in STEM disciplines. Funded by National Science Foundation.
http://www.quackwatch.org/index.html “Quackwatch is now an international network of people who are concerned about health-related frauds, myths, fads, fallacies, and misconduct.” From their mission statement. Hosted by a physician whose special expertise and interest is keeping people medically safe