So you have a fixed height container, and you want your text to be vertically centred, whether it be one line or many lines of text.  In every browser.   This is possible, as I just learned from this article.

For all modern browsers, and IE8 and IE9, the method uses display:table-cell.  For IE6 and IE7, the method described in the above article is used, which takes advantage of a height bug.

You HTML looks like this:

<div id="container">
	<div id="wrapper">
		<div id="content">
			Stuff and things
		</div>
	</div>
</div>

Your CSS looks like this:

#container
{
	width:200px;
	height:50px;
	background-color:red;
	*position:relative;
}
#wrapper
{
	background-color:green;
	height:inherit;
	display:table-cell;
	vertical-align:middle;
	*height:auto;
	*position:absolute;
	*top:50%;
}
#content
{
	background-color:blue;
	*position:relative;
	*top:-50%;
	color:white;
}

The result looks like this:

IE6

IE7

IE8

IE9 Beta

Google Chrome

And of course, this is not just constrained to text.  #content can be any variable-height block...