This worked for me.
I included an unordered list on my page twice. One div class="menu" id="vertical" the other to be centered was div class="menu" id="horizontal". Since the list was floated left, I needed an inner div to center it. See below.
<div class=menu id="horizontal">
<div class="fix">
Centered stuff
</div>
</div>
.menu#horizontal { display: block; float: left; margin: 0px; padding: 0 10px; position: relative; left: 50%; }
#fix { float: right; position: relative; left: -50%; margin: 0px auto; }