Mathematics

- The cookbook for R site provides some examples of ggplot2 graphics.
- A nice presentation by Scott Murray about D3 transition. This is most useful for the very beginner who wants to work with D3.
- Vega , a higher level data visualization tool.
- Interactive map from R by RMAP

- A quick list of useful R packages.
- Data Technologies for Statistical Analysis by Di Cook.
- Some knitr showcases by Yihui Xie.
- A nice effort to organize the searchable R documentation.

- Sources of government data
- Time series data from the Bureau of Labor Statistics
- World bank Data Bank
- Maps and boundary related data from Natural Earth
- Gapminder data about facts and figures.
- Some wonderful sources of data available online, bookmarked by Hadley Wickham.