MedlinePlus -- Useful for patient education, and health literacy, this site is a service offered by the U.S. National Library of Medicine. It provides information about diseases, conditions, and wellness issues in language non-experts can understand. "MedlinePlus offers reliable, up-to-date health information, anytime, anywhere, for free. You can use MedlinePlus to learn about the latest treatments, look up information on a drug or supplement, find out the meanings of words, or view medical videos or illustrations. You can also get links to the latest medical research on your topic or find out about clinical trials on a disease or condition."
Merck Manual, Professional Version -- first published in 1899 as a "service to the community," as of April 2015, the Merck manuals will no longer be published in print, but are now all digital. The Professional version retains its orientation to healthcare students and practitioners. There is a Consumer Version for patients and caregivers.