When we create websites with wordpress, there is a plugin you can upload to your plugins directory that creates a sitemap automatically for you…and also submits it to the major Search Engines each time you publish a page or post.
Other Ways To Create A Sitemap
For other applications (if you’ve built your website with Frontpage or Dreamweaver for example) a great FREE online sitemap creating tool is at http://www.xml-sitemaps.com/
On the same website you can find various other tools like the XML Sitemap Validator Tool. It will validate your xml sitemap and optionally ping Google to inform them of their location. It also tells you i there are any problems associated with your sitemaps, giving you time to make changes before you submit them to Google.
Also at http://www.xml-sitemaps.com/you have the option to ping Search Engines (Google, Yahoo, Ask.com, Moreover.com) with the whereabouts of your sitemap. They also recommend that you notify Google of your sitemaps via the Google Webmaster Tools.