Very powerful software for statistical analysis. All kinds of graphs. Scripting language included, for task automatization. Possibility to export to html or latex. I used it to automatically process questionnaire data and it did not take me more than a day (to learn to use stat-R and to generate these graphs and convert them in HTML format).
Analyzing Baseball Stats with R Brief and excellent introduction.
Using R for psychological research. A very simple guide to a very elegant package
Lecture notes on statistical data analysis (code included), ESSLLI 2005 (Linguistics)
S, catalogue of scripts The R users may benefit of a large number of programs written for S and available on internet, most of these programs can be used directly with R.