From PHP Magazine today:

JPGraph is a set of programs written in PHP that plots data into a wide range of graphs and formats the results. Licensed under the Trolltech QPL License, JPGraph is now at Version 1.17. Whatever your data, JPGraph can help you to view it graphically, letting you to see relations in more clearly. Such data visualization may not be important to a computer, but, to a person, it can make a lot of difference to analysis. In a new article on NewsForge, Glenn Mullikin takes JPGraph for a test and in looking at the graphs that result, comments on some of the formatting features offered by JPGraph. The bottomline, "Overall, I am not disappointed with JPGraph's function, but a few coupld offer more fine-grain control". Read on...

Unfortunately, he doesn't give out any of his code for the quite nice graphs that he developed, but it does give you a good idea of the power that lies in this library. Personally, whenever I need a more complex graph than just a few bars, I immediately reach for this...