<ul id="sortable">
    <li id="1">elem 1</li>
    <li id="2">elem 2</li>
    <li id="3">elem 3</li>
    <li id="4">elem 4</li>
</ul>

$(document).ready(function(){
    $('#sortable').sortable({
        update: function(event, ui) {
            var newOrder = $(this).sortable('toArray').toString();
            $.get('saveSortable.php', {order:newOrder});
        }
    });
});

Kilde: http://stackoverflow.com/questions/7097168/save-jquery-ui-sortable-positions-to-db