“Stacked Graphs – Geometry & Aesthetics” is by and large the best looking paper I have seen yet in the conference. Lee Byron and Martin Wattenberg have done a terrific job figuring out how to plot collections of time series. In particular, their technique works beautifully for collections where any particular member has a finite support: series start at zero, spike, and then return to zero forever after. In essence, they do a great job plotting population trends.
What I like about it (huge nerd that I am) is that they do a good job of quantifying the attributes they want to optimize, and the solutions are very simple. It never hurts to have gorgeous graphs in your paper either – they have the first effective bivariate color scale I have seen in a while. Check it out!