Centered and middled content ?
Do it this way :
<table style="width:100%">
<tr>
<td valign="middle" align="center">Table once ruled centering</td>
</tr>
</table>
Ha, let me guess .. you want DIVs ..
just make your first outter DIV behave like a table-cell then style it with vertical align:middle;
<div>
<p>I want this paragraph to be at the center, but I can't.</p>
</div>
div {
width:500px;
height:100px;
background-color:aqua;
text-align:center;
/* there it is */
display:table-cell;
vertical-align:middle;
}