In 1904 Charles Spearman published his seminal paper, "General Intelligence, Objectively Determined and Measured," in the American Journal of Psychology [PDF version] [HTML version]. This paper outlined the framework of a new statistical tool in support of Spearman's psychological theory of intelligence. The statistical method was factor analysis. In the century since it was introduced, factor analysis has become as integral to the development of psychological science as any method or procedure used in the study of human behavior.
To mark the centennial of the publication of Spearman's paper, a conference on the history, current issues, and future directions in factor analysis theory, methods, and applications was held at the University of North Carolina May 13-15, 2004. The conference was organized by Robert Cudeck and Robert MacCallum, with the assistance of an organizing committee, and will be hosted by the L. L. Thurstone Psychometric Laboratory. The conference program consisted of talks by 15 distinguished invited speakers, all internationally known for their past or current work in factor analysis or closely related methods.
Update: The book based on this conference was published in 2007 and can be obtained via this link.