Hadley Wickham's dplyr package is a great toolkit for getting data ready for analysis in R. If you haven't yet taken the plunge to using dplyr, Kevin Markham has put together a great hands-on video tutorial for his Data School blog, which you can see below. The video covers the five main data-manipulation "verbs" that dplyr provides: filter, select, arrange, mutate and summarise/group_by. (It also introduces the glimpse function, a handy alternative to str, that I had overlooked before.)
The video also provides an introduction to the %>% ("then") operator from magrittr, which you'll likely fund useful for many other applications in addition to dplyr. Also, Kevin's video works from an Rmarkdown script to show how dplyr works, and so serves as a mini-tutorial for Rmarkdown as well. It's well worth 40 minutes of your time. Also, check out Kevin's blog post linked below for links to many other useful dplyr resources.
Data School: Hands-on dplyr tutorial for faster data manipulation in R (via Peter Aldhous)