Sometimes it isn’t possible to leverage client-side charting possibilities via the use of Flash or javascript frameworks such as Sencha with their beautiful charting capabilites.

I once worked on a project whereby I needed to integrate charts into PDF output along with saving archive copies for future comparison in an easily downloadable format.

This is where a great library such as pChart comes is.  It is easy to implement, has advanced caching capabilities and needs only PHP, GD and FreeType PHP extensions installed on the host server to work which can be provided by most budget hosts these days.  The output possibilities are vast and varied and the result is equally beautiful to the above clientside alternatives, albeit without the interactivity.  However in the latest version of pChart there is the ability to allow automated image maps to be attributed to the charts and hence advanced interactivity can be achieved with the use of javscript.

I highly recommend you check it out.