Horizontal Menu with Vertical Submenu (HTML/CSS Only)

Question

I'm having a difficult time trying to make my submenu vertical instead of horizontal. Any help would be much appreciated.

HTML:

<ul id="menu">
  <li><a href="/" title="HOME">HOME</a></li>
  <li>
    <a href="/" title="ECO ENERGY">ECO ENERGY</a>
    <ul>
      <li><a href="/Evaluations" title="Evaluations">Evaluations</a></li>
      <li><a href="/Incentives" title="Incentives">Incentives</a></li>
      <li><a href="/HouseFiles" title="House Files">House Files</a></li>
      <li><a href="/UpdateSubmissions" title="Update Submissions">Update Submissions</a>/li>
    </ul>
    </li>
    <li>
      <a href="/" title="NEW HOMES">NEW HOMES</a>
      <ul>
        <li><a href="/NH" title="Evaluations">Evaluations</a></li>
      </ul>
    </li>
</ul>

CSS:

#menu {
  background-color: #206676;
  float: left;
  width: 100%;
  height: 60px;
}

ul#menu {
  font-size: 1.3em;
  font-weight: 600;
  margin: 0 0 5px;
  padding: 0;
  text-align: left;
}

ul#menu li {
  display: inline;
  list-style: none;
  padding-left: 15px;
  float: left;
}

ul#menu li a {
  background: none;
  color: #FFF;
  text-decoration: none;
}

ul#menu li a:hover {
  color: #FFF;
  text-decoration: none;
}

ul#menu ul {
  display: none;
}

ul#menu li {
  display: inline;
}

ul#menu li:hover ul {
  display: block;
}

ul#menu li:hover ul li a {
  display: block;
  color: red;
}

I have it to the point where I can toggle the colour when hovered over the main menu items, but just can't get them vertical.

fiddle HERE

Answer 1

ul#menu ul
{
    display:none;
    position:absolute;
    left:0;
    top:20px;
}
ul#menu li
{
    display:block;   
}

Most important changes. JSFIDDLE> http://jsfiddle.net/LSbvJ/ (You will have to tweak paddings, margins, text-align... but this is good start, I hope.)