Google Sitemaps

Google Sitemaps is an experiment in Web crawling by using Sitemaps to inform and direct Google search crawlers. Webmasters can place a Sitemap-formatted file on their Web server which enables Google crawlers to find out what pages are present and which have recently changed, and to crawl your site accordingly. Google Sitemaps is intended for all web site owners, from those with a single web page to companies with millions of ever-changing pages.
[Source: Adapted from Google Sitemaps FAQ]