This website provides a simple summary of the theme elements that can be set within ggplot2. There should be sufficient information here to change the default settings for graphs within the ggplot2 package.
Modern Applied Statistics with S (Statistics and Computing) W.N. Venables, B.D. Ripley
Interactive and Dynamic Graphics for Data Analysis: With R and GGobi (Use R) Dianne Cook, Deborah F. Swayne