This is an annotated list of books on R. It is idiosyncratic as it reflects my own preferences, and incomplete, as I list books that I have either bought or borrowed from libraries. The selection of titles is also biased because I have read mostly those books that are useful in my own research field.
Beckerman AP, Petchey OL (2012) Getting Started with R: An Introduction for Biologists. Oxford University Press, Oxford.
The simplest and most basic book on R. This very short book (128 pp.) will be useful for learning the absolute basics. You will most probably quickly read it once, and never touch it again. Read it if you can borrow it, but it is too expensive to be worthwhile buying it.
I have created a public Mendeley group with a list of books on R. I will add notes to the entries a.s.a.p. and tags.