Thanks to joemako (http://visguy.com/vgforum/index.php?action=profile;u=8)for Twitter-ing this the other day:
Pie charts and other circular visualizations (http://optional.is/required/2009/07/20/pie-charts-and-other-circular-visualizations/) - an entertaining, well-written, coherent analysis of why pie charts are overused, misused and suck in general. The author shows where non-circular visualizations are better than pie charts, and expands the topic by examining useful circular visualizations as well.
The author of Pie charts and other circular visualizations (http://optional.is/required/2009/07/20/pie-charts-and-other-circular-visualizations/) (mentioned previously) has another post about Polyphasic Sleep (http://optional.is/required/2009/06/27/polyphasic-sleep/) that has some cool circular visualizations that relate to time and the clock, and his own personal experiment to try different methods of sleeping.
Haters of pie charts will also enjoy this indictment of Apple's Steve Jobs misuse of wedges and 3D: Lies, damn lies, and Steve Jobs keynotes (http://www.guardian.co.uk/technology/blog/2008/jan/21/liesdamnliesandstevejobs)
Quite old post, but this article complements it so well.
http://www.datarevelations.com/circles-labels-colors-legends-and-sankey-diagrams-ask-these-three-questions.html
@Yacine: Excellent link. Really drives home the point of data visualization needs to be clear, understandable, and not "cute" just because it's possible.
Wapperdude