注明：如果要想要在IE6无限级的话需要写多一些JS，其他游览器都可以使用同段js
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>JavaScript下拉菜单</title>
    <style type="text/css">
        body,ul,li{margin:0; padding:0; font-size:12px; list-style:none;}
        #navigation {
            margin:20px; height:auto;
        }
        #navigation li {
            position:relative;width:130px; height:40px;border-bottom:1px solid #999999;
        }
        #navigation li a:link, #navigation li a:visited {
            display:block;
            text-decoration:none;
            color:#000;
            width:120px;
            height:40px;
            line-height:40px;
            background:#c5dbf2;
            padding-left:10px;
        }
        #navigation li a:hover {
            color:#fff;
            background: #000000;
        }
  #navigation li ul li a{filter:alpha(opacity=50);opacity:0.5;}
        #navigation li ul li a:hover {
            color:#fff;
            background:#6b839c;
        }
        #navigation li ul {
            display:none;
            position:absolute;
            top:0px;
            left:130px;
            width:120px;
        }
        #navigation li ul li ul {
            display:none;
            position:absolute;
            top:0px;
            left:130px;
            width:120px;
        }
    </style>
    <script type="text/javascript">
        function displaySubMenu(li) {
            var subMenu = li.getElementsByTagName("ul")[0];
            subMenu.style.display = "block";
        }
        function hideSubMenu(li) {
            var subMenu = li.getElementsByTagName("ul")[0];
            subMenu.style.display = "none";
        }
    </script>
 <!--IE6-->
     <script type="text/javascript">
        function displaySubMenu1(li) {
            var subMenu = li.getElementsByTagName("ul")[0];
            subMenu.style.display = "block";
        }
        function hideSubMenu1(li) {
            var subMenu = li.getElementsByTagName("ul")[0];
            subMenu.style.display = "none";
        }
    </script>
</head>
<body>
    <ul id="navigation">
        <li
            <a href="#">栏目1</a>   
            <ul>
                <li><a href="#">栏目1->菜单1</a></li>
            </ul>
        </li>
        <li
            <a href="#">栏目2</a>   
            <ul>
                <li><a href="#">栏目2->菜单1</a></li>
            </ul>
        </li>
        <li
            <a href="#">栏目3</a>   
            <ul>
                <li
                    <a href="#">栏目3->菜单1</a>
                    <ul>
                        <li><a href="#">菜单1->子菜单1</a></li>
                        <li><a href="#">菜单1->子菜单2</a></li>
                        <li><a href="#">菜单1->子菜单3</a></li>
                        <li><a href="#">菜单1->子菜单4</a></li>
                    </ul>
                </li>
            </ul>
        </li>
    </ul>
</body>
</html>