benlaw,
There is experimental support for charts in Spreadsheet::WriteExcel. The trouble I had was that I needed to hide the data sheet that the chart used so jmcnamara was kind enough to hack it in for me. I needed to use both modules in tandem (along with a bit of source code modification) to achieve everything I needed.

In a nutshell, you create a dummy chart with all the formatting you want and bind it to a datasheet with enough rows/cols to meet your real data, extract the binary representation of that chart to a bin file, and then insert the chart into your new spreadsheet and bind it to a datasheet with the real data. It wasn't a big PITA but it does take a little getting used to.