ggplot2 is a plotting system for R, based on the Grammar of Graphics, which tries to take the good parts of base and lattice graphics and none of the bad parts.
ggplot2.org - Site with links to Mailing List, few Books, and Video Tutorial.
ggplot2 0.9.3.1 - Beautiful Site with Docs, and Images of Functions for this Graphics Package.
ggplot2 : Elegant Graphics for Data Analysis - 201 Page PDF E-Book
ggplot2 Tutorial - quick 14 page PDF Tutorial with Examples