When presenting summarized data -- the data in the cells of a two-way ANOVA, for example -- it's always a good idea to visualize the uncertainty in the summaries. The natural way for statisticians is to use a boxplot, and ggplot2 makes that easy:
But Jarrett Byrnes, a marine community biologist, wanted to use a barplot, instead. (A boxplot shows more details of the distribution, but more people know how to read a barplot.) As he shows, it is possible, with a little extra work, add error bars to a barplot with ggplot2:
See the link below for the code: a great demonstration of the customization capabilities of ggplot2.
i’m a chordata! urochordata!: Let’s All Go Down to the Barplot! (Update Jan 2 2013: link to http://www.imachordata.com/?p=199 removed -- site compromised)