Today marks the hardcopy availability of the first book dedicated to R from O'Reilly, R in a Nutshell. In the familiar O'Reilly style, the cover is adorned with an illustration of an animal, in this case a harpy eagle:
The book is written by Joe Adler, a data analyst and the author of Baseball Hacks. In contrast to the many books that exist today that regard R through the prism of Statistics, Joe takes a much more general approach, treating R primarily as a language. (Disclaimer: I reviewed the book for O'Reilly, and a quote from me appears on the cover.) It's a great introduction for newcomers to the language, but also goes into enough depth that even longtime R users will find useful nuggets of information.
O'Reilly Media: R in a Nutshell