$(function(){
    $('#navigation li a').append('<span class="hover"></span>')
    $('#navigation .hover').css("filter", "alpha(opacity=00)");
    $('#navigation li a').hover(function(){ 
        // Stuff that happens when you hover on + the stop()
        $('.hover', this).stop().animate({
            'opacity': 1
        }, 700, 'easeOutSine')     
    }, function(){    
        // Stuff that happens when you unhover + the stop()
        $('.hover', this).stop().animate({
            'opacity': 0
        }, 700, 'easeOutQuad')        
    })
});