Self contained 16 column grid overlay. Toggle the overlay by pressing the 'G' key.

grid_overlay.js

$(function() {
  $('body').prepend('<div id="grid-overlay" style="display:none;width:100%;height:100%;position:fixed;z-index:99999999;margin-left:-20px;"></div>');
  $(new Array(30)).each(function() {
    $('#grid-overlay').append('<div style="float:left;width:60px;height:100%;margin-left:20px;background:rgba(255,153,153,0.2);"></div>');
  });
  keydown_show_grid = function(event) {
    if(event.which == 71) {
      $('#grid-overlay').toggle();
    }
  };
  $(document).bind('keydown', keydown_show_grid);
  $('input, textarea, select').focus(function() {
    $(document).unbind('keydown', keydown_show_grid);
  });
  $('input, textarea, select').blur(function() {
    $(document).bind('keydown', keydown_show_grid);
  });
});