Last week all the major search engine providers, announced that they were going to support a new specification at sitemap.org that allows them to auto discover your sitemap without you having to submit it:
Yahoo did a good job at summing up the advantages to putting your sitemap location in the robots.txt file.
All search crawlers recognize robots.txt, so it seemed like a good idea to use that mechanism to allow webmasters to share their Sitemaps. You agreed and encouraged us to allow robots.txt discovery of Sitemaps on our suggestion board. We took the idea to Google and Microsoft and are happy to announce today that you can now find your sitemaps in a uniform way across all participating engines.
If you want to see my implementation of this for my sitemap go to http://www.coderjournal.com/robots.txt. Further details about this can be found at http://sitemaps.org/protocol.htm or for your convenience I have included them below.
Specifying the Sitemap location in your robots.txt file
You can specify the location of the Sitemap using a robots.txt file. To do this, simply add the following line:
The <sitemap_location> should be the complete URL to the Sitemap, such as: http://www.example.com/sitemap.xml
This directive is independent of the user-agent line, so it doesn't matter where you place it in your file. If you have a Sitemap index file, you can include the location of just that file. You don't need to list each individual Sitemap listed in the index file.