Ask.com: http://submissions.ask.com/ping?sitemap=http%3A//www.domain.com/sitemap.xml
Google: http://www.google.com/webmasters/sitemaps/ping?sitemap=http:%3A//www.domain.com/sitemap.xml
Yahoo: http://search.yahooapis.com/SiteExplorerService/V1/updateNotification?appid=YahooDemo&url=http://www.domain.com/sitemap.xml
