See this fiddle: http://jsfiddle.net/manishie/CVYq6/
Basically, you take the regular bootstrap dropdown and change it from a ul to a div. But you keep the class name the same. Within that div, you can have whatever you want.
In this case you want two side by side lists, but you could have images, or any html you want.
Bootstrap works off the class name, so that when you click the toggle, whatever is in the .dropdown-menu class will appear.
HTML:
<div class="dropdown">
<a class="dropdown-toggle" data-toggle="dropdown" href="#">Dropdown trigger</a>
<div class="dropdown-menu" role="menu">
<ul>
<li>one</li>
<li>two</li>
<li>three</li>
<li>four</li>
</ul>
<ul>
<li>blah</li>
<li>blah blah</li>
<li>blah blah blah</li>
</ul>
</div>
</div>
CSS:
.dropdown-menu ul {
float: left;
}
.dropdown-menu ul:first-of-type {
border-right: 1px solid black;
padding-right:20px
}