IMPORTANT: Sitemaps.org Yahoo and Google announced a collaborative site called Sitemaps. (Due to start very soon!, 18 Nov 2006 I, believe)
Watch this Video.
A single way to submit sitemaps to both Google and Yahoo.
Not only are Google and Yahoo collaborating on this project, they’ve also issued an open invitation to the other search engines willing to join. Microsoft accepted that invitation and will jointly support Sitemaps.org and its efforts.
Maybe this is just the start of them working together, although they will be keeping to their own search algorithms for now :0
More about SiteMap