The Sitemaps protocol allows a webmaster to inform search engines about URLs on a website that are available for crawling. A Sitemap is an XML file that lists the URLs for a site. It allows webmasters to include additional information about each URL: when it was last updated, how often it changes, and how important it is in relation to other URLs in the site. This allows search engines to crawl the site more intelligently. Sitemaps are a URL inclusion protocol and complement robots.txt, a URL exclusion protocol.
How to Add a Google XML Sitemap to Your Web Page
Google XML Sitemaps And What To Do With It
Creating A Google Site Map
Google I/O 2008 - Sitemaps: Exposing Content in Web Apps
add sitemap tag to robots.txt
Local Wisdom \\Share EP9:Google Webmaster Central, XML-Sitemaps.com and you!
Which is better: an HTML site map or XML Sitemap?
Plone Google Sitemaps