The big three of search engines, Google, Yahoo & Microsoft Live, each announced yesterday evening that they have all agreed to support the use of sitemaps. With this agreement, a new version 0.9 of sitemaps has been released. The official home of sitemaps now resides at www.sitemaps.org.

Google has already has been accepting sitemaps through their Webmaster Tools. Yahoo is now also accepting files through their Site Explorer. Live is still testing and will be accepting them in the near future.
You can read their respective announcements from their blogs:

• Google Webmaster Central: Joint support for the Sitemap Protocol
  
• Google Blog: Search engines united
• Yahoo: Yahoo, Google and Microsoft join forces (really !!) behind Sitemaps
• Live: Microsoft, Google, Yahoo! Unite to Support Sitemaps

Sitemaps are an easy method for webmasters to inform search engines of their web site pages that are available for crawling. Sitemaps do not guarantee that a site will be indexed and included in the search engine results, but it will help the engines create a more effective and efficient crawl of a given site.