A voronoi treemap of the mammals, based on the Tree of Life dataset. Each polygon represents a species, with border color and thickness attempting to show cladistic groupings. The central yellow group is antelopes; warmly colored parts are ungulates. The blue/purple group at the top are various rodents, the irregular mint group to the left the carnivorae (the ToL does not have deeper subdivisions there), the white rectangle is the extinct triconodonts and the blue blob to the upper left is the primates.
The visualisation clearly has some way to go before being ready for prime time, but it is already appealing.
The image was calculated in Matlab. I used a variant of Balzer & Deussen's algorithm without the messy sample points and polygon extraction parts; I have to pay in terms of polygon quality instead, but I think I can fix that.