gRaphaël is a graphing library based on Raphaël, providing a way to draw pie, bar, line and dot charts, including support for interactive features such as dynamic labels and highlighting.
To draw a chart with gRaphaël you need to include on your page raphael.js, g.raphael.js and the script for the particular chart(s) you need (e.g. g.pie.js).
Then you can just create a raphael canvas, and draw your chart on it.
var r = Raphael("holder"); r.g.piechart(320, 240, 150, [55, 20, 13, 32, 5, 1, 2, 10]);
The documentation is a bit thin on the ground at the moment, but Raphaël is quite nice to work with and there are a few examples on the website to get you started.