Wickham et al's R packages are great, especially dplyr, and I think should be taught to new R users pretty much right off the bat. I find R's syntax to be a big hangup for new learners, especially on indexing and apply-to-each (sapply, mapply, just plain apply...), but dplyr really makes life much easier.

The %>% operator alone (which to be fair was originally from magrittr) is a great help. Not sure if this is my personal biases, but I always find it easier to read calls chained postfix-style.