presented in lightning talk, live demo form as part of a Rubyist's intro to R
at http://mtnwestrubyconf.org/2011/
by Alan Whitaker [http://twitter.com/digiduke]

code in eq.r

grab R here
  http://cran.r-project.org

or here
  http://www.rstudio.org/
    newly announced IDE, with remote server support and other cool stuff
  http://www.revolutionanalytics.com/downloads/
    company building commercial builds of R, but also free community edition with some speed enhancements

a few links
  R Reference card (very handy) http://cran.r-project.org/doc/contrib/Short-refcard.pdf
  an official intro http://cran.r-project.org/doc/manuals/R-intro.pdf
  UCLA R Starter Kit http://www.ats.ucla.edu/stat/r/sk/
  search http://www.rseek.org (googling "R <insert concept here>" is not always so helpful)

books for using / learning R
  Introductory Statistics with R, Peter Dalgaard http://amzn.to/gIPimD
    the classic book for learning R while brushing up stats
  R Cookbook, Paul Teetor http://amzn.to/h3UNYf
    brand new, but I like the structure and am finding some good refreshers and new things in here so far
  R in Action, Robert I. Kabacoff http://amzn.to/fTpCDr
    to be published, but available electronically with Manning Early Access Program

some "specialty" R books
  Data Manipulation with R, Phil Spector http://amzn.to/hxp8HC
    covers data frames, aggregation, etc
  Software for Data Analysis: Programming with R, John Chambers http://amzn.to/ev6oz1
    heavier tome, goes deeper on internals / data structures / coding packages