If you're just getting started with the R language, R user Pairach Piboonrungroj has published a handly list of 20 free R tutorials published by university departments. Included on the list: Getting Started with the R Data Analysis Package (by Norm Matloff), Getting Started with R (from York University), and An Introduction to R (by Phil Spector). Paraich also points to a concise one-page reference card of common R commands, which may be useful to print out and keep by your keyboard as you're learning R.
See the complete list of 20 free R tutorials at the link below.
Pairach Piboonrungroj: R Tutorials from Universities Around the World