Databases and evidence-based summaries
PubMed
http://www.ncbi.nlm.nih.gov/
You can use PubMed to search for abstracts from a large number of medical journals on your topic of interest. This service is provided free by the National Institute of Health in the United States.
Cochrane database
http://www.update-software.com/abstracts/mainindex.htm
Find abstracts of (rigorous) evidence-based reviews of health research, including depression. Additional information is available to organisations/people subscribing to the database.