For those who are still learning the basics of the R programming language, the following website might be interesting:
Another thing that might be interesting is the recently released R-library Swirl. The swirl R package is designed to simultaneously teach users statistics and the R programming language. In a typical swirl session, the user is required to load a package from the R console and chose from a menu of options the course he would like to take. Then he works through 10-15 minutes interactive modules, each covering a particular topic.
To install it, this is all you have to do in R:
Note however that the package is yet released and constantly fixed and updated. It is therefore recommended to update the version at least one ca month so you have full access to the latest features.
This is the official website of the package: http://swirlstats.com
You can find a blog post on the release of the new package on Simply Statistics: