I've used Spreadsheet::WriteExcel to create Excel files beore pretty quickly and easily. However, to get the most functionality out of Excel files (depending on how complicated the data you'll be using is - eg: graphs, formulas, etc...), you should look at Win32::OLE - which is what I use now to create (and modify) Excel files.

There is a good local tutorial for Win32::OLE and Excel at Using Win32::OLE and Excel - Tips and Tricks.