Adding a smoother line to a scatter plot in Data Visualization with ggplot2 / Overlay plots and Multiple plots
Combining a histogram and a density plot in Data Visualization with ggplot2 / Overlay plots and Multiple plots
Overlaying a line plot and a bar plot in Data Visualization with ggplot2 / Overlay plots and Multiple plots
Stacking data series in bars (stacked bar plot) in Data Visualization with ggplot2 / Overlay plots and Multiple plots
Creating a multiple pie/donut chart in Data Visualization with ggplot2 / Overlay plots and Multiple plots