jQuery实现侧边栏随窗口滚动

$(function() {
    var $sidebar   = $("#sidebar"),   
        $window    = $(window),   
        offset     = $sidebar.offset(),   
        topPadding = 15;   
  
    $window.scroll(function() {   
        if ($window.scrollTop() > offset.top) {   
            $sidebar.stop().animate({   
                marginTop: $window.scrollTop() - offset.top + topPadding   
            });   
        } else {   
            $sidebar.stop().animate({   
                marginTop: 0   
            });   
        }   
    });   
  
});   

进一步:http://css-tricks.com/scrollfollow-sidebar/