I am using Ruby 1.9 for this. I need to convert Ruby arrays to an Excel spreadsheet (xls) document.
I use two stones to export to readable in Excel format: Spreadsheet (can create / analyze .xls) and FasterCSV (faster, but as far as I remember, it does not work with .xls files)
I had excellent results with WriteExcel (which is the Ruby port of the Perl library the same name).
Csv files will be the fastest if you just want to export values