The article source:http://www.designchemical.com/lab/jquery-mega-drop-down-menu-plugin/getting-started/

The Mega Drop Down Menu plugin takes standard nested lists and turns them into horizontal mega menus.

A mega menu has several advantages over standard drop down menus, including:

• All options visible at the same time
• No scrolling and tricky mouse manoeuvres to see sub-menus fly out
• Using standard nested lists the groups can be easily structured and formatted with CSS

Create The HTML List

<ul id="mega-menu"><li><a href="#">Home</a></li>
 
<li><a href="#">Products</a>
<ul>
    <li><a href="#">Mobile Phones &#038; Accessories</a>
    <ul>
        <li><a href="#">Product 1</a></li>
        <li><a href="#">Product 2</a></li>
        <li><a href="#">Product 3</a></li>
 
    </ul>
</li>
    <li><a href="#">Desktop</a>
    <ul>
        <li><a href="#">Product 4</a></li>
        <li><a href="#">Product 5</a></li>
        <li><a href="#">Product 6</a></li>
 
        <li><a href="#">Product 7</a></li>
    </ul>
</li>
    <li><a href="#">Laptop</a>
    <ul>
        <li><a href="#">Product 8</a></li>
        <li><a href="#">Product 9</a></li>
 
        <li><a href="#">Product 10</a></li>
    </ul>
</li>
</ul>
</li>
<li><a href="#">Sale</a>
<ul>
    <li><a href="#">Special Offers</a>
    <ul>
        <li><a href="#">Offer 1</a></li>
        <li><a href="#">Offer 2</a></li>
        <li><a href="#">Offer 3</a></li>
    </ul>
</li>
    <li><a href="#">Reduced Price</a>
    <ul>
        <li><a href="#">Offer 4</a></li>
        <li><a href="#">Offer 5</a></li>
        <li><a href="#">Offer 6</a></li>
    </ul>
</li>
    <li><a href="#">Clearance Items</a>
    <ul>
        <li><a href="#">Offer 7</a></li>
        <li><a href="#">Offer 8</a></li>
        <li><a href="#">Offer 9</a></li>
 
    </ul>
</li>
</ul>
</li>
<li><a href="#">Contact us</a></li>
</ul>

Include Both The HoverIntent Plugin & The Mega Menu Plugin

<script type='text/javascript' src='js/jquery.hoverIntent.minified.js'></script>
<script type='text/javascript' src='js/jquery.dcmegamenu.1.2.js'></script>

Add The CSS

Below is a sample of basic/minimum CSS requirements for creating the mega menu layout.

#mega-menu-1 {
font: normal 13px Arial, sans-serif;
list-style: none;
position: relative;
padding: 0;
margin: 0;
}
#mega-menu-1 li ul, #mega-menu-1 .sub {
display: none;
}
#mega-menu-1 .sub ul {
display: block;
}
#mega-menu-1 {
background: #222;
width: 100%;
height: 40px;
position: relative;
}
#mega-menu-1 li {
float: left;
margin: 0;
padding: 0;
font-weight: bold;
}
#mega-menu-1 li a {
float: left;
display: block;
color: #fff;
padding: 12px 25px;
background: #222;
text-decoration: none;
}
#mega-menu-1 li.mega-hover a, #mega-menu-1 li a:hover {
background: #CCC;
color: #000;
}
#mega-menu-1 li .sub-container {
position: absolute;
}
#mega-menu-1 li .sub {
background: #efefef;
padding: 15px;
border: 1px solid #ccc;
}
#mega-menu-1 li .sub .row {
width: 100%;
overflow: hidden;
clear: both;
}
#mega-menu-1 li .sub li {
list-style: none;
float: none;
width: 170px;
font-size: 1em;
font-weight: normal;
}
#mega-menu-1 li .sub li.mega-hdr {
margin: 0 10px 10px 0;
float: left;
}
#mega-menu-1 li .sub li.mega-hdr.last {
margin-right: 0;
}
#mega-menu-1 li .sub a {
background: none;
color: #111;
padding: 7px 10px;
display: block;
float: none;
font-size: 0.9em;
}
#mega-menu-1 li .sub li.mega-hdr a.mega-hdr-a {
padding: 5px 15px;
margin-bottom: 5px;
background: #6B6B6B;
text-transform: uppercase;
font-weight: bold;
color: #fff;
}
#mega-menu-1 li .sub li.mega-hdr a.mega-hdr-a:hover {
color: #000;
}
#mega-menu-1 .sub li.mega-hdr li a {
padding: 4px 5px;
font-weight: normal;
}
#mega-menu-1 .sub li.mega-hdr li a:hover {
color: #a32403;
background: #efefef;
}
#mega-menu-1 .sub ul li {
padding-right: 0;
}
#mega-menu-1 li .sub-container.non-mega .sub {
padding: 10px;
}
#mega-menu-1 li .sub-container.non-mega li {
padding: 0;
width: 190px;
margin: 0;
}
#mega-menu-1 li .sub-container.non-mega li a {
padding: 7px 5px 7px 22px;
}
#mega-menu-1 li .sub-container.non-mega li a:hover {
color: #a32403;
background: #efefef;
}

Initialise The Mega Menu

To initialise the mega menu with the default settings – 3 sub menus per row and fade in speed of “fast” – use the following code:

jQuery(document).ready(function($) {
    jQuery('#mega-menu').dcMegaMenu();
});