(function($){
    $.fn.extend({
        droplinemenu: function(configs) {
            var configs = $.extend({               
                over: 200,
                out: 100,
                rightdown:'css/down.gif'
            },configs||{});
            this.find(">ul").addClass("dropmenu");
            this.find("ul li:has(ul)").addClass('hasmenu').find(">a").append("<img class='downarrowclass' src='"+configs.rightdown+"'>");
            var currentobj;
            return $('li.hasmenu').hover(function(){                
                if ($.browser.msie) {//清除ie下生成的overflow:hidden
                    $(this).parent("ul").css({'overflow': 'visible'});
                }
                $(this).find(">ul").stop(true, true).css('top',$(this).height()).slideDown(configs.over);
            },function(){  
                $(this).find(">ul").stop(true, true).slideUp(configs.out);
            });
        }
    });
})(jQuery);

* {margin:0;padding:0}
.droplinebar{
     position: absolute;
    z-index: 20;
    width: 700px;
}
.droplinebar ul.dropmenu {
position: relative;
}
.droplinebar ul{
width: 100%;
float: left;
font: bold 13px Arial;
background: #242c54 url(bluedefault.gif) center center repeat-x; /*default background of menu bar*/
}
.droplinebar ul li{
    float:left;
}
.droplinebar ul ul {
    width: 700px;
    display:none;
    z-index: 100;
    position:absolute;
    left:0;
    background: #303c76;
    zoom: 1;
}
.droplinebar ul li a{
    float: left;
    color: white;
    padding: 9px 11px;
    text-decoration: none;
    display:block;
}
.droplinebar ul li.hasmenu a img {border:none;margin-left:5px;}
.droplinebar ul li a:hover, .droplinebar ul li .current{ /*background of main menu bar links onMouseover*/
color: white;
background: transparent url(blueactive.gif) center center repeat-x;
} 
/* Sub level menu links style */
.droplinebar ul li ul li a{
font: normal 13px Verdana;
padding: 6px;
padding-right: 8px;
margin: 0;
border-bottom: 1px solid navy;
}
.droplinebar ul li ul li a:hover{ /*sub menu links' background color onMouseover */
background: #242c54;
}

<link rel="stylesheet" type="text/css" href="css/droplinebar.css" />
<script type="text/javascript" src="js/jquery.min.js"></script>
<script src="js/droplinemenu.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function(){
    $("#mydroplinemenu").droplinemenu();
});
</script>
<div id="mydroplinemenu" class="droplinebar">
<ul>
<li><a href="http://www.dynamicdrive.com/">Home</a></li>
<li><a href="http://www.dynamicdrive.com/style/">CSS Examples</a>
  <ul>
  <li><a href="#">Activities 1</a></li>
  <li><a href="#">Activities 2</a></li>
  <li><a href="#">Activities 3</a>
      <ul>
      <li><a href="#">Water Sports 1</a></li>
      <li><a href="#">Water Sports 1</a></li>
      <li><a href="#">Water Sports 1</a></li>
      <li><a href="#">Water Sports 1</a></li>
      </ul>
    </li>
  <li><a href="#">Activities 4</a></li>
  </ul>
</li>
<li><a href="http://tools.dynamicdrive.com">Tools</a></li>
<li><a href="http://www.javascriptkit.com/">JavaScript</a>
  <ul>
  <li><a href="#">Traveling 1</a></li>
  <li><a href="#">Traveling 2</a></li>
  <li><a href="#">Traveling 3</a></li>
  <li><a href="#">Traveling 4</a>
      <ul>
      <li><a href="#">Africa 1</a></li>
      <li><a href="#">Africa 2</a></li>
      <li><a href="#">Africa 3</a></li>
      <li><a href="#">Africa 4</a>
          <ul>
          <li><a href="#">Kenya 1</a></li>
          <li><a href="#">Kenya 2</a></li>
          <li><a href="#">Kenya 3</a></li>
          <li><a href="#">Kenya 4</a></li>
          <li><a href="#">Kenya 5</a></li>
          </ul>
        </li>
      </ul>
    </li>
  <li><a href="#">Traveling 5</a></li>
  </ul>
</li>
<li><a href="http://www.cssdrive.com">Gallery</a></li>
</ul>
</div>

$(document).ready(function(){
    var configs_over = 200,configs_out = 100;
    $("#mydroplinemenu").find(">ul").addClass("dropmenu").find("li:has(ul)").addClass('hasmenu').find(">a").append("<img class='downarrowclass' src='css/down.gif'>");
    $('.dropmenu li.hasmenu').hover(function(){             
        if ($.browser.msie) {//清除ie下生成的overflow:hidden
            $(this).parent("ul").css({'overflow': 'visible'});
        }
        $(this).find(">ul").stop(true, true).css('top',$(this).height()).slideDown(configs_over);
    },function(){  
        $(this).find(">ul").stop(true, true).slideUp(configs_out);
    });
});