SO 23866327

add_action('admin_menu', 'add_auxiliary_menu');
add_action("wp_ajax_callbackFunction","callbackFunction");
add_action("wp_ajax_nopriv_callbackFunction","callbackFunction");

function add_auxiliary_menu()
{
    add_menu_page(
        'TB',
        '<span style="color:#e57300;">Thickbox</span>',
        'edit_pages',
        'thickbox-press-this',
        'menu_page_content',
        '', // icon default for empty
        1  // create before Dashboard menu item
    );
}

function menu_page_content()
{
    ?>
    <div id="icon-post" class="icon32"></div>
    <h2>Press-This in a Thickbox</h2>

    <div style="width:50%; padding: 5px;" class="updated" >
        <p><a class="button-secondary" href="#" id="open-tb"><?php _e( 'Press not this' ); ?></a></p>
    </div>
    <p><?php echo_users(false); ?></p>
    <script type="text/javascript">
    jQuery(document).ready(function($) {
        $("#open-tb").click(function() {
            $.post("<?php echo admin_url("admin-ajax.php"); ?>", {"action": "callbackFunction"}, function(response) {
                console.dir(response);
            });
        });
    });
    </script>
    <?php
}

function callbackFunction(){
    echo_users();
    die();
}

function echo_users($ajax=true)
{
    $blogusers = get_users();
    $br = $ajax ? '|' : '<br/>';
    foreach ($blogusers as $user) {
        echo $user->user_email.$br;
    }
}