Swirl, and interactive tutorial. It is an installable package that will run through RStudio.
**Cookbook for R **
A very useful online tutorial, especially when it comes to graphs
Another very useful website, here you will find clear and to the point instructions on how to create new variables, recode the values of existing ones, assign missing cases etc.
Those are the ones I use, including R-Ladies, a group aiming to promote gender diversity in the R community.