R

Books about R
Sells printed copies of free software manuals, including the official R introduction (tutorial) and both reference manuals. [Network Theory Ltd.]
http://www.network-theory.co.uk/R/

Comprehensive R Archive Network
Network of FTP and Web servers around the world that store identical, up-to-date, versions of r code, documentation.
http://www.cran.r-project.org/

An Introduction to R
Derived from an original set of notes describing the S and S-Plus environments. [PDF]
http://cran.r-project.org/doc/manuals/R-intro.pdf

Omegahat R Package Download Area
Over 30 R packages, libraries, released as part of Omegahat project. Many are bindings to other languages: Python, Gtk, XML; COM, SOAP, etc. Most can also be used with S-Plus. [Open Source, BSD-like]
http://www.omegahat.org/download/R/packages/

RPy
R from Python. Simple, robust, Python interface to R; manage all kinds of R objects and execute arbitrary R functions, including graphics. Converts all R errors to Python exceptions. Use any R module from within Python. [Open Source, GPL]
http://rpy.sourceforge.net/

Universal GUI for R
JGR is a universal and platform independent GUI for R. It features many tools like, advanced editor, object browser, flexible data input/output, package management and many more innovative features.
http://www.rosuda.org/JGR/

Statistical Programming with R: Part 2. Functional Programming and Data Exploration
Now that the data is correct, delves into functionality of system. Text, code samples, graphics. [developerWorks] <small>(October 7, 2004)</small>
http://www-106.ibm.com/developerworks/linux/library/l-r2/

Statistical Programming with R: Part 1. Dabbling with a Wealth of Statistical Facilities
Intermediate introduction, abilities. Text, code samples, graphics. [developerWorks] <small>(September 21, 2004)</small>
http://www-128.ibm.com/developerworks/linux/library/l-r1/

Server Clinic: R Handy for Crunching Data
Beginner introduction with code samples, further reading. [developerWorks] <small>(July 30, 2003)</small>
http://www-128.ibm.com/developerworks/linux/library/l-sc16.html