Your website should have two kinds of sitemaps: user-friendly index of pages and a search-engine sitemap.

The user-friendly index of pages is for your visitors to find information quickly. It is also used by search engines to find pages on your site. These site maps increase the weight of your pages on search engines because they contain page links and keywords.

The other sitemap is an XML document that you submit to Google, MSN and other search engines so the links get added to those search engines.

For more information read “How Sitemaps Can Improve Your Search Engine Rankings” by Ross Dunn.