"Articles on Statistical Computing - R" from the Social Science Computing Cooperative, at the University of Wisconsin-Madison
"Cookbook for R," by Winston Chang
"Getting Started in Data Analysis Using Stata and R," by Oscar Torres-Reyna, Princeton University
"Quick-R - 'Accessing the Power of R'"
"R for Data Science," by Garrett Grolemund and Hadley Wickham
"R - "Quick List of Useful R Packages"
"RStudio Cheat Sheets"
"R for SAS and SPSS Users," by Robert A. Muenchen, the University of Tennessee (.pdf)
"R for Stata Users," by Matthieu Gomez , Princeton University
"Resources to Help You Learn and Use R," from UCLA's Academic Technology Services
"Tidyverse - R Packages for Data Science," by Hadley Wickham
"Using R and RStudio for Data Management, Statistical Analysis, and Graphics" (Second Edition) (.pdf)
"Using R to Analyse Key UK Surveys," from the UK Data Service (.pdf)