I have just completed DataCamp‘s Introduction to R course.
I really liked the course. I was challenged by it at times which I think is a good thing (It shows I’m climbing a learning curve).
I also wanted to pass on R-Fiddle. I am a big fan of JSFiddle from my web development background. I was happy to see an R equivalent. StatAce is another interesting tool. Especially if you are wanting to do something in R but can’t install it on your machine.