I follow Flowing Data closely and feel compelled to tell the forum about a Python product, PyIMSL Studio, my company offers at no charge for non-commercial use. So, while I feel stabbing pains of guilt at spamming the forum with a software promotion, again, its free and cool stuff:
http://www.vni.com/campaigns/pyimslstudioeval/
The big thing we offer is Python wrappers to our collection of hundreds of mathematical and statistical algorithms written in C. You can install our Python distribution (which includes things like Numpy, matplotlib, xlrd, etc), or you can just install our math/stat/data manipulation packages into your existing Python area.
On a side note, I have contributed some examples to the matplotlib gallery and one in particular this forum might find interesting is here: http://matplotlib.sourceforge.net/examples/api/radar_chart.html
Here, I was playing with ways of visualizing the differences in factor loading estimates across different scenarios for an air pollution source apportionment model. matplotlib can certainly produce beautiful graphics, but this forum in particular has inspired me to start investigating web-centric visualization tools like Processing.
Anyway, I hope you find our product useful for doing the analyses behind cool visualizations!