Always makes me think: http://www.perceptualedge.com/articles/visual_business_intelligence/expressing_proportions.pdf
Not sure I agree so much with this edition, but I like that he is taking on those goofy unit charts (and I missed the Unit Charts are for Kids essay the first time around http://www.perceptualedge.com/articles/visual_business_intelligence/unit_charts_are_for_kids.pdf )
Healthy Algorithms 