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Flags by Colours is an interesting web project (by Shahee Ilyas) that shows flags of over 200 nations as color piecharts.
All of the flag piecharts are listed on one page, hovering mouse over particular chart presents the name of the country, clicking the charts shows the actual flag. There is also a big piechart showing color proportions of all flags combined.
The flag data is gathered from sources such as The World Factbook and Wikipedia.
If you find Flags by Colour interesting you can also check out Flagid, the website for identifying flags.