Put this code into a script section into a common HTML head include file:

$(document).ready(function() {

  $('table').each(function() {
    var $table = $(this);

    var $button = $("<button type='button'>");
    $button.text("Export to spreadsheet");
    $button.insertAfter($table);

    $button.click(function() {
      var csv = $table.table2CSV({delivery:'value'});
      window.location.href = 'data:text/csv;charset=UTF-8,'
                            + encodeURIComponent(csv);
    });
  });
})

Note:

• Requires JQuery and table2CSV (i.e. put script references before the script above)
• “table” selector is a JQuery selector and can be adjusted to suit your needs
• Only works in browsers with full “Data URI” support (Firefox, Chrome, Opera) but not in IE (which only supports Date URIs for embedding binary image data into a page)
• For full browser compatibility you would have to use a slightly different approach that requires a server side script (e.g. a Java Servlet) to “echo” the CSV. Maybe I will blog about that in another post.