R project - R is a free software environment for statistical computing and graphics. It compiles and runs on a wide variety of UNIX platforms, Windows and MacOS.
R Studio - RStudio IDE is a powerful and productive user interface for R. It’s free and open source, and works great on Windows, Mac, and Linux.
R Cookbook - Download link to an introductory book to learning R.
R Tutorial Blog - A blog with lots of R tutorials.
Coursera's R course - Recorded R lessons from Coursera on youtube.
R Intro Book - Another great introductory pdf book on R.