It's free and open source. I have haven't--thanks, Steve W.--used it in my classes yet, but it could well be excellent for graduate students.
Some other R-related links that may be of interest:
Where to get R and its documentation: "The Comprehensive R Archive Network".
Other: Springer books about R, R-Commander--a GUI for R, recent Fordham "Conference on Quantitative Social Science Research Using R", "Revolutions", "R Tutorial Series: Hierarchical Linear Regression".