CSS center content inside div

To center a div, set it’s width to some value and add margin: auto.

#partners .wrap {
    width: 655px;
    margin: auto;
}

EDIT, you want to center the div contents, not the div itself. You need to change display property of h2, ul and li to inline, and remove the float: left.

#partners li, ul, h2 {
    display: inline;
    float: none;
}

Then, they will be layed out like normal text elements, and aligned according to text-align property of their container, which is what you want.