PieChart

As of Version 7.0, PieChart is part of the built-in Mathematica kernel.

generates a pie chart of the positive values

PieEdgeStyle	Automatic	style of the lines
PieExploded	None	control of the radial positions of wedges
PieLabels	Automatic	list of labels for each pie wedge
PieOrientation	Automatic	ordering of pie wedges
PieStyle	Automatic	list of styles for each pie wedge

A pie chart of four values:

Needs["PieCharts`"]

A pie chart of four values:

Out[2]=