Find the last time drupal content of a particular content type or list of content types was updated (without views). Sometimes people like this kind of thing, apparently.

custom.module

<?php

/**
 * Returns a single "Last Updated" date.
 * 
 * $types -- an array of content type machine names. Defaults to 'page'.
 */
function custom_last_updated($types = array('page')) {
	$query = db_select('node', 'n');

	$query
		->condition('type', $types, 'IN')
		->condition('status', 1, '=')
		->fields('n', array('changed'))
		->orderBy('changed', 'DESC')
		->range(0, 1);

	$result = $query->execute()->fetchField();

	$last_changed = '<div class="last-updated">Last Updated: ' . format_date($result, 'custom', 'l, F jS, Y') . '</div>';

	return $last_changed;
}