pie chart, that cannot be displayed BETTER in some other type of chart," is a quote Wikipedia attributes to the late, great statistician John Tukey, (I've found no original source for the quote). It gets worse when Excel and/or graphic designers start adding chart junk of 3-D projections in hope of adding more visual interest.
If you insist on using pie charts, Benjamin Starr at Visual News offers some history and sensible guidelines for using pie charts.
First, as the lead-in graphic above illustrates, display no more than five categories in a pie chart. Many small areas are difficult to compare.
Of course, we've posted some pie charts here and had some fun with them.