WP_check_user_role

function check_user_role( $role, $user_id = null ) {
    if(is_numeric($user_id))
        $user = get_userdata($user_id);
    else
        $user = wp_get_current_user();

    if(empty($user))
        return false;

    return in_array( $role, (array) $user->roles );
}