zurb foundation center content in the grid

Edit November 2015: In Foundation 6 check out Typography Helpers

Edit April 2014: In Foundation 5 check out Utility classes.

Original answer:

Use the text-center class.

<div class="row">
    <div class="twelve columns text-center"><br />
        <img src="https://stackoverflow.com/questions/12079049/img_06.jpeg" alt="slide image">
    </div>
</div>

Source: https://github.com/zurb/foundation/pull/224