How would I select this with CSS?

Lets say I have the following..

<div>
    <div>
        <div>
            <div></div>  <<<Select this one..
            <div></div>  <<<Not this one..
            <div></div>  <<<Select this one..
            <div></div>  <<<Select this one..
        </div>
    </div>
</div>

How would I select those 3 divs without adding any classes or ids? Is this even possible?

You can use the :not() and :nth-child() pseudo-classes.

<!-- begin snippet: js hide: false --> <!-- language: lang-css --> 
div > div > div > div:not(:nth-child(2)){
  color: red;
}
<!-- language: lang-html --> 
<div>
  <div>
    <div>
      <div>Test</div> 
      <div>Test</div>
      <div>Test</div>
      <div>Test</div>
    </div>
  </div>
</div>
<!-- end snippet -->

Demo in jsFiddle

Note: For ie8 support, you could use the same selector in jQuery and style your element that way.

<!-- begin snippet: js hide: true -->
<!-- language: lang-js --> 
$("div > div > div > div:not(:nth-child(2))")
	.css("background-color", "yellow")
<!-- language: lang-html --> 
<div>
  <div>
    <div>
      <div>Test</div> 
      <div>Test</div>
      <div>Test</div>
      <div>Test</div>
    </div>
  </div>
</div>

<!-- External Resources -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<!-- end snippet -->