Also, with the ArcSegment control and the RotateTransform transform, it shouldn't be that awful to roll your own
http://www.charlespetzold.com/blog/2008/01/Mathematics-of-ArcSegment.html
http://www.codeproject.com/KB/WPF/TransformationsIntro.aspx
http://www.codeproject.com/KB/WPF/PieChartDataBinding.aspx