By Ray A.

I have found this works well:

1. Paste this url into Google's url adrress box after changing "www.website.com" to the name of your web site:
http://www.google.com/webmasters/sitemaps/ping?sitemap=http://www.website.com/sitemap.xml

2. Hit Go or Enter

3. You will be taken to a page which says:
Sitemap Notification Received

Your Sitemap has been successfully added to our list of Sitemaps to crawl. If this is the first time you are notifying Google about this Sitemap, please add it via http://www.google.com/webmasters/tools/ so you can track its status. Please note that we do not add all submitted URLs to our index, and we cannot make any predictions or guarantees about when or if they will appear.

Also:
YAHOO
http://search.yahooapis.com/SiteExplorerService/V1/updateNotification?appid=YahooDemo&url=http://www.website.com/sitemap.xml

ASK
http://submissions.ask.com/ping?sitemap=http://www.website.com/sitemap.xml

best wishes,
Ray

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