The R Manuals
https://cran.r-project.org/manuals.html
Contributed Documentation
https://cran.r-project.org/other-docs.html
note: no longer actively maintained
Learning Statistics with R
https://learningstatisticswithr.com
R for Psychological Science
https://psyr.djnavarro.net
Modelling and visualizing data using R: A practical introduction
https://www.danielnettle.org.uk/r-modelling/
Cookbook for R
http://www.cookbook-r.com
Tutorials by William King
https://ww2.coastal.edu/kingw/statistics/R-tutorials/
Using R for Psychological Research
http://personality-project.org/r/r.guide.html
An Introduction to R
https://intro2r.com
YaRrr! The Pirate’s Guide to R
https://bookdown.org/ndphillips/YaRrr/
R for Data Science
https://r4ds.had.co.nz/
Coding Club: A Positive Peer-Learning Community
https://ourcodingclub.github.io
Modern Statistics for Modern Biology
https://web.stanford.edu/class/bios221/book/index.html
Tidy Modeling with R
https://www.tmwr.org
ANOVA in R
https://www.statsandr.com/blog/anova-in-r/
R-DAVIS (R-Data Analysis & Visualization In Science)
https://gge-ucd.github.io/R-DAVIS/
UCLA Institute for Digital Research & Education Website
https://stats.idre.ucla.edu
Tweet by Terry McGlynn (@hormiga) on resources for learning R
https://twitter.com/hormiga/status/1316166483139944449