The CDC is a great source of timely as well as background information on diseases of all kinds and health in general. Since it is a government agency, the reports, images, and other content on the site are freely reproducible and not subject to copyright.
Here are some particularly useful sub-sections of the CDC website:
The NIH is the nation's medical research agency, producing and supporting research in all areas of human health. It is the largest source of medical funding in the world, providing grants to universities and research institutes all over the country, including St. Mary's.
Here are some important sub-sections of the NIH website: