Something very significant is happening out there. The three major search engines, Yahoo!, MSN, and Google are coming together in support of of the Sitemaps protocol. http://www.sitemaps.org/
Sitemaps are an easy way for webmasters to inform search engines about pages on their sites that are available for crawling. In its simplest form, a Sitemap is an XML file that lists URLs for a site along with additional metadata about each URL (when it was last updated, how often it usually changes, and how important it is, relative to other URLs in the site) so that search engines can more intelligently crawl the site. Using the Sitemap protocol does not guarantee that web pages are included in search engines, but provides hints for web crawlers to do a better job of crawling your site.
Google Blog informs that Google published Sitemap 0.84 XML protocol last year. The protocol was launched under Attribution-ShareAlike Creative Commons License. However a new version of the protocol is the one which is supported by Google, Yahoo! and MSN.