Yo te Recomiendo la librería libchart.
Código PHP:
$chart = new PieChart(500, 250);
$dataSet = new XYDataSet();
$dataSet->addPoint(new Point("Mozilla Firefox (80)", 80));
$dataSet->addPoint(new Point("Konqueror (75)", 75));
$dataSet->addPoint(new Point("Other (50)", 50));
$chart->setDataSet($dataSet);
$chart->setTitle("User agents for www.example.com");
$chart->render("generated/demo3.png");
http://naku.dohcrew.com/libchart/pages/samplecode/
Saludos