Facebook's IPO. The social network graphic is featured on Page 7 of the IPO filing. His graphic was featured on mashable and R-bloggers not too long ago. The graphic is of Facebook connections between city centers around the world. Paul used an ingenious method of color transparency and great circle arcs to display the social network graph.
This is just one of the really cool things you can do with R. Not only is R used as a visual medium but also to calculate the great circle paths. This is really neat to see R in such a high profile setting. If you want to learn more about R you can read an IEORTools post about R links for beginners on World Statistics Day. Also there are many books that you can buy on R programming at the IEORTools Online Store.