<style type="text/css">
.wraptocenter {
    display: table-cell;
    text-align: center;
    vertical-align: middle;
    width: ...;
    height: ...;
}
.wraptocenter * {
    vertical-align: middle;
}
/*\*//*/
.wraptocenter {
    display: block;
}
.wraptocenter span {
    display: inline-block;
    height: 100%;
    width: 1px;
}
/**/
</style>
<!--[if lt IE 8]><style>
.wraptocenter span {
    display: inline-block;
    height: 100%;
}
</style><![endif]-->
<div class="wraptocenter"><span></span><img src="..." alt="..."></div>

http://www.brunildo.org/test/img_center.html

Centering (horizontally and vertically) an image in a box

XHTML