ScapeToad - Open Source Cartogram Generator
ScapeToad provides an amazingly easy to use interface for creating cartograms. Accepting shapefiles directly as input, it has a wide variety of fine-tunable settings in addition to its presets. The ability to utilize multiple layers as weights also seems like a pretty exciting feature. Written entirely in java, it's platform-independent, another plus for mac and / or linux GIS users.
[caption id="attachment_127" align="alignnone" width="300" caption="Above: The counties of Washington State."][/caption]
What is so cool about this program is that not only does it use shapefiles as an input, but it generates shapefiles as output as well. A SizeError attribute is also generated to allow a user to easily control map symbology using GIS software. In addition to this, one can also export as an SVG directly to use in a graphics editor.
The cartogram below was generated using the percentage of a county's total area covered by state routes. The lighter colors indicate a smaller distortion in size while the darker colors indicate a larger distortion in size. Note the I-5 corridor in Western Washington is heavily affected using this criteria.
[caption id="attachment_128" align="alignnone" width="300" caption="Above: The result. "][/caption]
ScapeToad - http://chorogram.choros.ch/scapetoad/index.php
Data (WA DOT) - http://www.wsdot.wa.gov/