There are many sites available online that offer useful information.  It is generally helpful to note the type of website as generally indicated by the web site address:

.gov --- Government sponsored
.org --- From a not-for-profit agency
.edu --- Sponsored by a university
.com --- Developed by a for-profit company which may be selling a product. 
 

"Top Ten" Most Useful Websites

The Medical Library Association has found the following web sites particularly useful (sites are listed in alphabetical, NOT ranked, order):

• Cancer.gov
• Centers for Disease Control and Prevention (CDC)
• Familydoctor.org
• Healthfinder
• HIV InSite
• Kidshealth ®
• Mayo Clinic
• MEDEM: an information partnership of medical societies
• MEDLINEplus ( English | Spanish )
• NOAH: New York Online Access to Health

Consumer and Patient Health Information Section , a section of the Medical Library Association , has a useful list of links to specialized and general health information.