Hans Rosling, a doctor and researcher at Sweden's Karolinska Institute, spoke recently at the "TED @ State" conference on popular myths of differences between the "developed" and "developing" worlds, particularly regarding health issues. In his convincing, compelling and entertaining presentation Dr. Rosling uses imperial data set into graphs animated to show changes over time. This is a great example of the use of visualizations to improve understanding.
Dr. Rosling uses a tool called Gapminder to create these wonderful animated visuals. This organization allows others to submit data sets for possible upload to the Gaminder site.
Gapminder also created the Motion Chart Gadget to be used with Google's spreadsheet tool, for a more simple, DYI, version.