This answer doesn't necessarily scale but only requires minor adjustments as the list grows. Semantically it might seem a little counter-intuitive since it is two lists, but aside from that it'll look the way you want in any browser ever made.
ul {_x000D_
float: left;_x000D_
}_x000D_
_x000D_
ul > li {_x000D_
width: 6em;_x000D_
}
_x000D_
<!-- Column 1 -->_x000D_
<ul>_x000D_
<li>Item 1</li>_x000D_
<li>Item 2</li>_x000D_
<li>Item 3</li>_x000D_
</ul>_x000D_
<!-- Column 2 -->_x000D_
<ul>_x000D_
<li>Item 4</li>_x000D_
<li>Item 5</li>_x000D_
<li>Item 6</li>_x000D_
</ul>
_x000D_