I have been very impressed with ChartDirector, even though it costs $99. I'm trying to get my boss to pay for it. I've been using a trial version and am pleased with the results. I've also seen that they have great customer support.

I've also checked into a couple of very good Open Source modules:

SVG::TT::Graph
Changing the symbols is easy (for me anyway) Modifying the spacing between data points is very difficult (i.e. not starting our data directly on the y axis) This also outputs text as text elements, thus allowing me to generate PDFs generated from it in which the text is searchable.

Chart::Clicker
Modifying the spacing between data points is easy (i.e. not starting our data directly on the y axis) Changing the symbols is extremely difficult. Text is output as drawing commands. PDFs generated from the output will not have searchable text.

Hope this helps!

UPDATE:

ChartDirector works great for raster (e.g. PNG) or for SVG (i.e. vector) graphics.

I'm specifically working with SVG files. To output SVG using ChartDirector call the method enableVectorOutput() after creating the chart object, then use a file name ending in '.svg' when you output the file:

$chart_obj->enableVectorOutput();

. . .

$chart_obj->makeChart('chart.svg');
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