
Creating site map is nothing but showing direction to search engines while crawling your site.site map lists all the pages present in website along with page information.site map helps in crawling the page faster and easy way.
Google Sitemap Generator is a tool installed on your web server to generate the Sitemaps automatically. Unlike many other third party Sitemap generation tools, Google Sitemap Generator takes a different approach: it will monitor your web server traffic, and detect updates to your website automatically.
Site maps are present in XML,RAR and HTML format.But for search engines XML is most suitable format.You can create custom site map but many freewares are available.
Following is the list of Google map generator sites:
http://www.auditmypc.com/free-sitemap-generator.asp
http://www.vigos.com/products/gsitemap/
http://enarion.net/google/phpsitemapng/
http://www.automapit.com/googlesitemaps.html
http://www.freesitemapgenerator.com/
http://www.neuroticweb.com/recursos/sitemap/
http://www.addme.com/ror-sitemap-generator.htm
http://www.scriptsocket.com/sitemaps.php
http://www.seoutility.com/it/tools/google/sitemap_generator.aspx (Italian)
http://www.sitemapsubmit.net/generate-sitemap
http://www.smart-it-consulting.com/internet/google/submit-validate-sitemap/
Use It :)