Altra possibilità con i menu parzialmente sovrapposti...

codice:
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>CSS drop-down menu</title>
<style type="text/css">
div.menu-bar {
	position: relative;
	left: 0;
	top: 0;
	/* menu header width and height */
	height: 30px;
	width: 90%;
	margin: 0;
	padding: 0;
}
 
/* horizontal menu */

div.menu-bar ul {
	margin: 0;
	padding: 0;
	position: absolute;
	left: 0;
	top: 0;
	height: 100%;
	width: 100%;
	list-style-type: none;
	background-color: #fffabf;
	overflow: visible;
}

div.menu-bar ul li {
	display: block;
	float: left;
	height: 100%;
	/* menu header's items width */
	width: 119px;
	border-right: 1px #5d5636 solid;
}

div.menu-bar ul li span, div.menu-bar ul li a {
	display: block;
	height: 100%;
	width: 90%;
	line-height: 30px;
	padding: 0 0 0 10%;
	cursor: pointer;
}

div.menu-bar ul li span, div.menu-bar ul li a, div.menu-bar ul li a:link,
div.menu-bar ul li a:visited, div.menu-bar ul li a:active {
	font-family: Times New Roman;
	font-size: 17px;
	font-style: italic;
	text-decoration: none;
	background-color: #fffabf;
	color: #5d5636;
}

/* vertical sub-menus */

div.menu-bar ul li ul {
	position: static;
	height: auto;
	/* vertical-menus width */
	width: 160px;
	border: 1px #666666 solid;
	background-color: #dddddd;
}

div.menu-bar ul li ul li {
	position: relative;
	left: 0;
	top: 0;
	display: block;
	height: 28px;
	width: 100%;
	background-color: transparent;
	border: none;
	float: none;
}

div.menu-bar ul li:hover ul li span, div.menu-bar ul li:hover ul li a,
div.menu-bar ul li ul li a:link, div.menu-bar ul li ul li a:visited,
div.menu-bar ul li ul li a:active {
	display: block;
	height: 100%;
	width: 96%;
	padding: 0 0 0 4%;
	line-height: 28px;
	background-color: transparent;
	color: #000000;
	font-family: georgia, serif;
	font-size: 11px;
	font-style: normal;
	font-weight: normal;
}

/* vertical sub-sub-menus */

div.menu-bar ul li:hover ul li ul {
	/* sub-sub-menu position is relative to its parent */
	position: absolute;
	top: 6px;
	left: 156px;
}

/* mouse-over effects: up to 6 sub-levels (you can add more sub-levels, if you want) */

div.menu-bar ul li:hover span, div.menu-bar ul li:hover a {
	color: #220000;
	background-color: #eeeabe;
}

div.menu-bar ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover a,
div.menu-bar ul li:hover ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover ul li:hover a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover a {
	background-color: #cccccc;
	color: #000000;
}


div.menu-bar ul li:hover ul li:hover ul li span,
div.menu-bar ul li:hover ul li:hover ul li a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li a,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li span,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li a {
	background-color: transparent;
	color: #222222;
}

div.menu-bar ul li ul, div.menu-bar ul li:hover ul li ul, div.menu-bar ul li:hover ul li:hover ul li ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li ul {
	display: none;
}

div.menu-bar ul li:hover ul, div.menu-bar ul li:hover ul li:hover ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul,
div.menu-bar ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul li:hover ul {
	display: block;
}

/* an arrow on the right side of menu's folders */

span.menu-nav:after, a.menu-nav:after {
	content: "\00BB";
	float: right;
	margin-right: 8px;
}

</style>
</head>

<body>
<h1>CSS drop-down menu</h1>

<div class="menu-bar">
  <ul>[*]
      Home
    [*]
      JavaScript
      <ul>[*]
          Link
        [*]
          Submenu
          <ul>[*]
              Submenu
              <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]                
                  Submenu
                  <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]
                      Submenu
                      <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]<span onclick="alert('!');">JavaScript function</span>[*]
                          Submenu
                          <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]Link[/list]
                        [*]Link[*]Link[*]Link[/list]
                    [/list]
                [*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]Link[*]Link[*]Link[/list]
            [*]Link[*]<span onclick="alert('!');">JavaScript function</span>[/list]
        [/list]
    [*]
      CSS
      <ul>[*]
          Submenu
          <ul>[*]Link[*]Link[*]Link[/list]
        [*]
          <span onclick="alert('!');">JavaScript function</span>
        [*]
          Submenu
          <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[/list]
        [*]
          Link
        [*]
          Link
        [/list]
    [*]
      <span>Documents</span>
      <ul>[*]
          Submenu
          <ul>[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]<span onclick="alert('!');">JavaScript function</span>[*]Link[*]Link[*]Link[*]Link[/list]
        [*]
          Submenu
          <ul>[*]Link[*]Link[*]<span onclick="alert('!');">JavaScript function</span>[/list]
        [*]
          Link
        [/list]
    [*]
      <span>About Us</span>
      <ul>[*]
          <span onclick="alert('!');">JavaScript function</span>
        [/list]
    [/list]
</div>



[ Page content here ]</p>

</body>
</html>