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. It takes care of many of the fiddly details that make plotting a hassle (like drawing legends) as well as providing a powerful model of graphics that makes it easy to produce complex multi-layered graphics.
ggplot2 documentation is now available at docs.ggplot2.org.
You are welcome to ask ggplot2 questions on R-help, but if you’d like to participate in a more focussed mailing list, please sign up for the ggplot2 mailing list:
You must be a member to post messages, but anyone can read the archived discussions.
(You’ll need to make sure you have the most recent version of R to get the most recent version of ggplot)
Books about ggplot2
The R Graphics Cookbook by Winston Chang provides a set of recipes to solve common graphics problems. Read this book if you want to start making standard graphics with ggplot2 as quickly as possible.
ggplot2: Elegant Graphics for Data Analysis by Hadley Wickham describes the theoretical underpinnings of ggplot2 and shows you how all the pieces fit together. This book helps you understand the theory that underpins ggplot2, and will help you create new types of graphic specifically tailored to your needs. You can read sample chapters and download the book code from the book website.
You might also find the following presentations useful: