The designer Antonio Lupetti's "The Cost of Spam: CO2 Emissions" is a lovely illustration of a rather dirty problem: the environmental impact of the astonishingly high number spam emails generated around the world.
One thing I like about this is that it gets Eyjafjallajökull back in the conversation—it has really been upstaged, disaster-wise, by that oil spill in the Gulf.
If you're curious, it looks like the data come from a 2009 McAffee study and CommTouch's most recent quarterly report.