I am going to go against the flow here and point out that Spreadsheet::WriteExcel recently added initial support for charting (Gnumeric and OpenOffice.org compatible). While I know that Excel charting itself is quite primitive, it does have the advantage of being commonly available, so your chart users can build on your efforts.

"The Spreadsheet::WriteExcel Perl module can be used to create a cross-platform Excel binary file. Multiple worksheets can be added to a workbook and formatting can be applied to cells. Text, numbers, formulas, hyperlinks, images and charts can be written to the cells.

The file produced by this module is compatible with Excel 97, 2000, 2002, 2003 and 2007.

The module will work on the majority of Windows, UNIX and Mac platforms. Generated files are also compatible with the Linux/UNIX spreadsheet applications Gnumeric and OpenOffice.org."