A study by Jay Fournier and Rob DeRubeis shows antidepressants work best for severe depression, but provide little to no benefit otherwise.
Link to the article on Penn's home page: http://www.upenn.edu/pennnews/article.php?id=1791
Link to NY Times article: http://www.nytimes.com/2010/01/06/health/views/06depress.html
Excerpt from Penn's home page:
Penn Study Shows...