align text vertical center in div with css

Basic:
#box { height: 90px; line-height: 90px; }

A more versatile approach:
div { width: 250px; height: 100px; line-height: 100px; text-align: center; }
 span { display: inline-block; vertical-align: middle; line-height: normal; }

Display Table: 

div { display: table; width: 250px; height: 100px; text-align: center; }
span { display: table-cell; vertical-align: middle; }