html: <div id="parent"> <div id="child">Content here</div> </div> css: #child {line-height: 200px;}
Vertical centering is achieved by giving the child div (the one containing the text) a line-height larger than the font-size. Some also set a height equal to the line-height on this div, but I haven't found it necessary.
This will work to vertically center a single line of text, but won't work for multiple lines of text.
Note: Additional styles not related to the above have been used to make this demo more presentable.