This list will grow over time

• http://www.r-tutor.com
• http://statistics.ats.ucla.edu/stat/r/
• http://a-little-book-of-r-for-time-series.readthedocs.io/en/latest/
• http://sphaerula.com/legacy/R/index.html
• http://www.statmethods.net/   Good for an introduction to R