Vinu Thomas points out a nice looking PHP charting library on his blog today - pChart.

Looking for some good looking graphs without having to pay for a library or resort to Flash graphs? Try creating your own using pChart. pChart is a PHP class oriented framework designed to create aliased charts. This project focuses on allowing developers to generate great looking graphs by increasing rendering quality introducing an aliasing algorithm.

It uses GD to create the graphs, so just about any PHP distribution out there will support it (if you're not sure, make a phpinfo() page to check out your setup). There's even some example graphs so you can get an idea of what some of the end results could be.