These are links that you'll likely refer to over & over throughout your work in R. In a general sense, R is a programming language, so to make it useful for your particular work you'll likely need to extend its capabilities. These links will help.
These website contain lists of packages for extending R's capabilities beyond basic statistics, or enabling it to work in a cluster or distributed environment.
Have you ever done a search for "R"? If so then you know how frustrating it can be to find relevant sites that address your question. This list includes a handful of search engines specific to R.
This is a list of PDF cheat sheets that you can print out & keep handy as a reference while working with R.
As you practice with R programming, you're going to want data to work with. Here's a collection of data sets that are freely available. There are a handful of data set sizes here.