A site map has often also been called a "crawler page". If well designed this page will help both Search Engine robots (aka spiders or crawlers) and human visitors find your pages quickly.

From the robot's perspective, a site crawler page is nothing more than a complete list of all the pages of the site, in the form of hyperlinks to these pages. Robots will follow these links and index all the pages of the site, provided the crawler page is easy to find and crawl.

Also, develop a site map for your site because it's just as useful to human visitors: these nifty little navigation buttons that act as signposts often don't tell a lot about what will be found on the page. To a human visitor some may sound downright cryptic, which won't increase the likelihood of being clicked. On your site map, include short descriptions of the page content in the form of a hyperlink text anchor. If you've already visited our page on linking strategies, you'll understand the importance of these text anchors so don't forget to include your main search term of the page in the anchor.

Link the site map straight from the home page and display the link clearly visible, so that humans can easily visit it and use it as a site summary.

When you add new pages to your site, always update the site map. That way, spiders will always index the new content quickly.

You can find a good example of a site map on this site.