This is the web site for the Center for Disease Control, and it has up-to-date and accurate information about vaccines, travel medicine and a variety of disease screenings.

This is the web site for general medical knowledge, in an easy-to-understand format.  It contains information regarding standard medical care, health conditions and some alternative medical practices.  It is not an in-depth source of information, but may be substantial enough for most purposes.

This is the web site for the Mayo Clinic compendium on thousands of medical diseases and conditions.  It is written at a somewhat higher level of complexity, but is far more in-depth and useful.

This is the web site for the United States Preventative Services Taskforce.  It is the official compendium for approved screening for every imaginable health condition.  While there is a summary of the most common such screenings, here on our website, this is the comprehensive web site for all such screening.  Generally, if the USPST makes a recommendation for a screening test, the insurance companies abide by those recommendations. 

This is the United States government web site regarding cancer; including information about cancers, staging, treatments and a list of cancer centers in the United States.

This is the United States government web site for the US Food and Drug Association.  It is an exhaustive compendium regarding drugs, medical devices, food safety and a long list of other subjects.

This is the United States government web site for general medical information on diseases and conditions.  I find the Mayo Clinic site more informative and easier to navigate, but this may be an excellent second source of information.