About R
R is a general-purpose, command-line based, environment for working with data. R is based on a functional approach to working with vectors and matrices of data. R is a convenient environment for processing, analyzing, and plotting data. The statistical tests and model building facilities of R are rivaled by no other single application.

 
Getting Started

• Excellent tutorial an nearly every aspect of R (c/o Rob Kabacoff)
• R Cookbook
• R time series tutorial
• R Concepts and Data Types presentation by Deepayan Sarkar
• The R Wiki
• An Introduction to R
• Import / Export Manual
• R Reference Cards
• Introduction to R by Vincent Zoonekynd
• KickStart
• Hints on plotting data in R
• Regression and ANOVA
• Appendices to Fox Book on Regression
• JGR a Java-based GUI for R [Mac|Windows|Linux]
• A Handbook of Statistical Analyses Using R(Brian S. Everitt and Torsten Hothorn)

 
Searching for Information

• RSeek
• R Site Search

 
R with Geographic Data

• Geographically weighted regression
• Geostats with geoR
• DCluster, splancs, spdep and spatstat packages available on CRAN
• GRASS6 - R Interface
• Interesting thread on the use of kriging variance

 
Excellent Tutorials by David Rossitier
http://www.itc.nl/personal/rossiter/pubs/list.html#pubs_m_R

 
Misc. Articles

• When Summary Stats Aren't Enough
• Why "dynamite plots" are a bad idea
• Many examples of plotting data in R
• Notes on R
• Scientific Graphing applications
• Ideas on how to make more informative axis in a plot
• Tips on R graphics
• Color space visualization