A cartogram is a map where the area depicted depends on the value of a variable instead of the actual geographic size within the boundaries of the area. Worldmapper has a large collection of cartograms (366, with more added all the time). Here’s a cartogram of number of plant species by country:
In addition to the graphic image, which can be downloaded by right-clicking on it and choosing “Save Image”, you can also download the data used to create the maps in Excel format and OpenDoc format. Some maps include animations of the map morphing from a standard map to a cartogram, and/or can be downloaded in PDF poster format (missing for some of the newer maps).
More info about cartograms is available at Cartogram Central.