两级导航菜单树jquery插件特效调用方法：$.jq51menu("#menubox","div.submenu");  这里的#menubox 是主菜单的ID，div.submenu是子菜单的ID。两级导航菜单树的样式很丑陋，懒人建站嘛，俺够懒，就懒得写好看的界面了。还是劳你大驾自己动手设计下界面和css把。^_^^_^

jquery代码：
<script src="http://lib.sinaapp.com/js/jquery/1.4.2/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(document).ready(function(){
    jQuery.jq51menu = function(menuboxid,submenu){
        
        var menuboxli = $(menuboxid+" li");
        menuboxli.eq(0).find(submenu).show();
        menuboxli.click( function () {
            $(this).addClass("thismenu").find(submenu).show().end().siblings("li").removeClass("thismenu").find(submenu).hide();
             return false;
        });
        
    };
    
    $.jq51menu("#menubox","div.submenu");

});
</script>

html代码：
<div id="menubox">
    <ul>
        <li><a href="http://www.51xuediannao.com/">懒人建站</a>
            <div class="submenu">
                <a href="http://www.51xuediannao.com/js/nav/">导航菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
            </div>
        </li>
        <li><a href="http://www.51xuediannao.com/js/slide/">焦点幻灯片</a>
            <div class="submenu">
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
            </div>
        </li>
        <li><a href="http://www.51xuediannao.com/js/gg/">广告代码</a>
            <div class="submenu">
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
            </div>
        </li>
        <li><a href="http://www.51xuediannao.com/js/texiao/">网页特效</a>
            <div class="submenu">
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
                <a href="#">二级子菜单</a>
            </div>
        </li>
    </ul>
</div>