Swirl: Swirl is an R package that allows you to learn R interactively in the R console.
R for Data Science from Garrett Grolemund and Hadley Wickham: An excellent introduction to data science via R by two heavyweights of the R community, it is broken down into 5 parts, corresponding to steps in the data science process: Explore, Wrangle, Program, Model, and Communicate. You’ll learn the “tidy” approach to data, and immediately use libraries such as dplyr, tidyr, and ggplot2. Some basic knowledge of R can be helpful, but isn’t absolutely necessary. It’s also available as a book.
Advanced R from Hadley Wickham: A companion website to the book of the same name, it introduces more advanced features (and quirks) of the R language, e.g. style, exception handling, functional programming, R’s C interface, etc.
Data Science Specialization: A comprehensive, challenging, 10-part course from Johns Hopkins University & Coursera. Covers R, the data science workflow, stats, and some machine learning.
R Tutorial: A basic intro to R and stats from the University of Georgia, Department of Mathematics.
Sharp Sight Labs: A useful blog with short tutorials on the nuts and bolts of data analysis in R, with a focus on tidyverse tools and on developing fluency.
The Analytics Edge: Semester-long course from MIT & edX. Covers stats/DS using real-world examples.
Quick-R: A website dedicated to helping individuals with some background in statistics transition to R.