Cartograms are maps which distort area to show some other variable, such as population size. Chloropleth maps use different colours or colour intensities to show information, and proportional symbol maps use a circle, or other shape of a different size to convey information – for example a larger person to show a larger population.

There are plenty of online tools to help you generate colourful and visually interesting maps to show statistical data - here are a few suggested by the ECF list. 

http://www.delicious.com/day_jess/ecampaigning+mapping+visualization

This article summarises a discussion on the eCampaigning Forum email list. Thanks to everyone who contributed.