Depression

Depression by Harvard Medical School
Depression by the National Institute of Mental Health
Depression by John M. Grohl, Psy.D. 
Men and Depression by the National Institute of Mental Health

Schizophrenia

Schizophrenia by the National Institute of Mental Health
Biological Origin of Schizophrenia by Harvard Medical School
Scientists Move Closer to Understanding Schizophrenia's Cause by Benedict Carey, The New York Times

Stress

Stress
The Danger of Stress by Melinda Wenner, Scientific American
7 Startups that Want to Improve Your Mental Health by CNN

Gambling

Gambling
How the Brain Gets Addicted to Gambling by Scientific American
NIH on the Inside: Gambling Addiction by National Institutes of Health