Additional examples can be found on the respective help pages of each geometric attribute, or on the webpages of the ggplot
document. Here are some useful links to such pages:
The qplot function: http://docs.ggplot2.org/current/qplot.html
Histograms: http://docs.ggplot2.org/current/geom_histogram.html
Density plots: http://docs.ggplot2.org/current/geom_density.html and http://docs.ggplot2.org/current/stat_density.html
Bar charts: http://docs.ggplot2.org/current/geom_bar.html
Scatterplots and Bubble charts: http://docs.ggplot2.org/0.9.3.1/geom_point.html