The corrplot package is a graphical display of a correlation matrix, confidence interval. It also contains some algorithms to do matrix reordering.
Michael Friendly (2002). Corrgrams: Exploratory displays for correlation matrices. The American Statistician, 56, 316--324.
D.J. Murdoch, E.D. Chow (1996). A graphical display of large correlation matrices. The American Statistician, 50, 178--180.
The plotcorr function in the ellipse package and corrgram function in the corrgram package has some similarities.