ggplot2 is a very elegant language for describing how to draw your data. Two great books for interested parties: the R Graphics Cookbook [0] which has tons of ggplot2 examples and gets you plotting immediately; and ggplot2: Elegant Graphics for Data Analysis [1] written by the author of the ggplot2 library and providing a very thorough description of this implementation of the "Grammar of Graphics".
[0] http://amzn.to/1AhyEdE
[1] http://amzn.to/1B4OSq9