NY Times graphic artists Amanda Cox and Shan Carter created this beautiful interactive geographical histogram showing how different groups voted during the 2008 Democratic Presidential Primaries .
It's data visualization at its absolute best - taking a mass of data, and presenting it as an easy to interpret stacked bar chart. The killer feature is the use of subtle animation to create a compelling narrative, resulting in a graphic that is an absolute joy to use and experience. Clicking down the levels of education, for example, reveals a gradual swing to Obama, whilst browsing by age group shows the hold that Obama and Clinton exert over younger and older age groups respectively.