Wordpress - Change page title in admin area

add_filter('admin_title', 'my_admin_title', 10, 2);

function my_admin_title($admin_title, $title)
{
    return get_bloginfo('name').' • '.$title;
}

You could also do a str_replace on $admin_title to remove "— WordPress" and change "‹".

Look at the top of the wp-admin/admin-header.php file to see what is going on by default.