Swirl
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
Quick-R
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.
R-Ladies
Those are the ones I use, including R-Ladies, a group aiming to promote gender diversity in the R community.