Data visualization
For those who have not read the seminal works of Tufte and Cleveland, please hang your heads in shame. To salvage some sense of self-worth, you can then head over to Solomon Messing’s blog where he is starting a series on data visualization based on the principles developed by Tufte and Cleveland (with R examples).
The classics are also worth reading, and remain relevant despite the 20 or 30 years that have elapsed since they appeared.