Charts in django Web Applications
Another choice is CairoPlot.
We picked matplotlib over the others for some serious graphing inside one of our django apps, primarily because it was the only one that gave us exactly the kind of control we needed.
Performance generating PNG's was fine for us but... it was a highly specialized app with less than 10 logins a day.
Open Flash Chart 2
http://teethgrinder.co.uk/open-flash-chart-2/
python library http://btbytes.github.com/pyofc2/
kybi