I'm trying to build a collection of good chart resources. The problem with the PHP libraries in PECL and PEAR is that they are still alpha/beta. I you have used a specific library/tool please add them to this wiki and if possible please add the experience you had with it.
Reviewed from smashingmagazine:
Open Flash Chart, Flash
PlotKit, JS/MochiKit (BSD)
(uses Google excanvas (Apache license) for more general 2d lib support
) We've had some good success with this
Google Charts, image