jQuery sortSelect v1.0.0
Installation and basic usage
First you must include the jQuery library and the orderSelect plugin.
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7/jquery.min.js"></script>
<script type="text/javascript" src="sortSelect.jquery.js"></script>

<script type="text/javascript">
$(function(){
      $('select[name="select-1"]').sortSelect();
});
</script>
Demo 1
Group the select field options by their first letter.
Code:

$('select[name="select-1"]').sortSelect();
Result:

Demo 2
Group the select field options by a letter on a custom position.
In the demo we will group by the 5-th letter.
Code:

$('select[name="select-2"]').sortSelect({ position: 5 });
Result:

Demo 3
Group the select field options by their 5-th letter and make the first option a label for the field.
Code:

$('select[name="select-3"]').sortSelect({ position: 5, defaultSelected: true });
Result: