ScapeToad is an interesting, free, stand-alone cartogram software for Mac, Windows (and available platform independent). ScapeToad 1.1 is available for download under a GPL license.
Classical thematic mapping displays spatial patterns of theme or series data depicted on familiar reference maps of standard land-area polygons, which are typically distorted only by the selected projection. A cartogram is a map in which some thematic mapping variable – such as travel time or Gross National Product – is substituted for land area. The geometry or space of the map is distorted in order to convey the information of this alternate variable. There are two main types of cartograms: area and distance cartograms. To see examples, WorldMapper.org provides a nice collection of cartograms.
(from the ScapeToad website) “The visualization of social phenomena through classical thematic mapping often leads to unsatisfying representations… Cartograms are a well-known technique used to compensate for this inconvenience by breaking the link between statistical regions and their topographical areas. Consequently, this liberates one visual variable (that of polygon size) for a more relevant use, such as the representation of the relative social importance of these regions (usually measured by the size of their populations), while leaving intact their topological relations.”