jquery实现的一个多级下拉菜单，理论上支持无限多的层级，文件结构简单，适合新手参考。
完整代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>jquery多级下拉菜单-www.jb200.com</title>
<style>
/* navigation style */
#keleyi-com-nav{
height: 39px;
font: 12px Geneva, Arial, Helvetica, sans-serif;
background: #2D2D2D;
border: 1px solid #323232;
border-radius: 3px;
min-width:500px;
margin-left: 0px;
padding-left: 0px;
}
#keleyi-com-nav li{
list-style: none;
display: block;
float: left;
height: 40px;
position: relative;
border-right: 1px solid #323232;
}
#keleyi-com-nav li a{
padding: 0px 10px 0px 30px;
margin: 0px 0;
line-height: 40px;
text-decoration: none;
border-right: 1px solid #636161;
height: 40px;
color: #FFF;
text-shadow: 1px 1px 1px #66696B;
}
#keleyi-com-nav ul{
background: #f2f5f6;
padding: 0px;
border-bottom: 1px solid #DDDDDD;
border-right: 1px solid #DDDDDD;
border-left:1px solid #DDDDDD;
border-radius: 0px 0px 3px 3px;
box-shadow: 2px 2px 3px #ECECEC;
-webkit-box-shadow: 2px 2px 3px #ECECEC;
-moz-box-shadow:2px 2px 3px #ECECEC;
width:170px;
}
#keleyi-com-nav .site-name,#keleyi-com-nav .site-name:hover{
padding-left: 10px;
padding-right: 10px;
color: #FFF;
background: url(http://www.jb200.com/phtml/jqmenu/4/logo.png) no-repeat 10px 5px;
width: 160px;
}
#keleyi-com-nav .site-name a{
width: 129px;
overflow:hidden;
}
#keleyi-com-nav li.facebook{
background: url(http://www.jb200.com/phtml/jqmenu/4/facebook.png) no-repeat 9px 12px;
}
#keleyi-com-nav li.facebook:hover {
background: url(http://www.jb200.com/phtml/jqmenu/4/facebook.png) no-repeat 9px 12px #010101;
}
#keleyi-com-nav li.yahoo{
background: url(http://www.jb200.com/phtml/jqmenu/4/yahoo.png) no-repeat 9px 12px;
}
#keleyi-com-nav li.yahoo:hover {
background: url(http://www.jb200.com/phtml/jqmenu/4/yahoo.png) no-repeat 9px 12px #010101;
}
#keleyi-com-nav li:hover{
background: #010101;
}
#keleyi-com-nav li a{
display: block;
}
#keleyi-com-nav ul li {
border-right:none;
border-bottom:1px solid #DDDDDD;
width:170px;
height:39px;
}
#keleyi-com-nav ul li a {
border-right: none;
color:#6791AD;
text-shadow: 1px 1px 1px #FFF;
border-bottom:1px solid #FFFFFF;
}
#keleyi-com-nav ul li:hover{background:#DFEEF0;}
#keleyi-com-nav ul li:last-child { border-bottom: none;}
#keleyi-com-nav ul li:last-child a{ border-bottom: none;}
/* Sub menus */
#keleyi-com-nav ul{
display: none;
visibility:hidden;
position: absolute;
top: 40px;
}
/* Third-level menus */
#keleyi-com-nav ul ul{
top: 0px;
left:170px;
display: none;
visibility:hidden;
border: 1px solid #DDDDDD;
}
/* Fourth-level menus */
#keleyi-com-nav ul ul ul{
top: 0px;
left:170px;
display: none;
visibility:hidden;
border: 1px solid #DDDDDD;
}
#keleyi-com-nav ul li{
display: block;
visibility:visible;
}
#keleyi-com-nav li:hover > ul{
display: block;
visibility:visible;
}
</style>
<!--[if IE 7]>
<style>
#keleyi-com-nav{
margin-left:0px
}
#keleyi-com-nav ul{
left:-40px;
}
#keleyi-com-nav ul ul{
left:130px;
}
#keleyi-com-nav ul ul ul{
left:130px;
}
</style>
<![endif]-->
<script type="text/javascript" src="http://www.jb200.com/pmedia/jquery/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$("#kel"+"eyi-com-nav li").hover(
function () {
$(this).children('ul').hide();
$(this).children('ul').slideDown('fast');
},
function () {
$('ul', this).slideUp('fast');
});
});
</script>
</head>
<body>
<ul id="keleyi-com-nav">
<li class="site-name"><a href="http://www.jb200.com"> </a></li>
<li class="yahoo"><a href="http://www.jb200.com">导航菜单</a>
<ul>
<li><a href="http://www.jb200.com/a/bjac/veugsmw9.htm">导航菜单二级分类 »</a>
<ul>
<li><a href="http://www.jb200.com">1</a></li>
<li><a href="http://www.jb200.com/a/bjac/r55i6646.htm">2</a></li>
<li><a href="http://www.jb200.com">3</a></li>
<li><a href="http://www.jb200.com">导航菜单三 »</a>
<ul>
<li><a href="http://www.jb200.com">导航菜单4</a></li>
<li><a href="http://www.jb200.com/a/bjac/c6gu08gm.htm">1</a></li>
</ul>
</li>
</ul>
</li>
<li><a href="http://www.jb200.com">1</a></li>
<li><a href="http://www.jb200.com">2</a></li>
</ul>
</li>
<li class="facebook"><a href="http://www.jb200.com">翻页</a>
<ul>
<li><a href="http://www.jb200.com">1</a></li>
<li><a href="http://www.jb200.com">2</a></li>
</ul>
</li>
</ul>
</body>
</html>