This article recommends 33 free books which will teach you the basics of R, how to produce amazing plots, how to apply R to lots of disciplines, and how to efficiently program in R.
A. Hotho, R. Jäschke, C. Schmitz, and G. Stumme. Proceedings of the First Conceptual Structures Tool Interoperability Workshop at the 14th International Conference on Conceptual Structures, page 87-102. Aalborg, Aalborg Universitetsforlag, (2006)