General Health & Medicine (including pets) from the U.S. National Library of Medicine: www.medlineplus.gov; from the American Academy of Family Physicians: familydoctor.org.
Heart Health from the American Heart Association's patient site: www.hearthub.org; from the National Coalition for Women with Heart Disease: womenheart.org
Healthy Lifestyle Guides
Diet and Nutrition-
From the Academy of Nutrition and Dietetics: eatright.org has nutritional information, food safety, vegetarian information as well as focused information for other groups including athletes. From Harvard: hsph.harvard.edu/nutritionsource is a fantastic source for planning healthy meals.
From the Centers for Disease Control and Prevention: cdc.gov/physicalactivity has easily adapted weekly workout plans in addition to many fitness resources.The American Council on Exercise has step-by-step instructional photos, workouts, & guilt-busting advice: www.acefitness.org.
Diabetes resources can be found at diabetes.org as well as on the site of the National Diabetes Education Program: www.ndep.nih.gov. The latter will match a researcher with appropriate resources for one's specific age, diabetes status & race.
Current breast cancer research can be found at breastcancer.org; thousands of questions are answered on the John Hopkins site: breastcenter.org
Researching emotional and psychological issues should begin with the American Psychiatric Association's site: healthyminds.org; for support, including live online groups, check out dbsalliance.org from the National Depression and Bipolar Support Alliance.