MedlinePlus is one of the best sources for consumer health information on the web.
Created by the National Library of Medicine, it provides short summaries on a wide range of conditions and then links out to high quality information created by non-profits, government groups, and other organizations. They also include links to information in other languages when possible. A Spanish version of the site is also available.
MedlinePlus also includes drug and supplement information, news alerts, and anatomy and surgery videos.