Getting Into Google by Jill Whalen reports Dan Crow, director of crawl systems at Google, saying that Google is releasing a new META tag named 'unavailable_after'.

The 'unavailable_after' tag will allow you to tell Google when Googlebot should no longer crawl that page. This tag comes in handy when you have a limited time offer promotional page, and on this page, the promotion will expire on a specific date. By using the 'unavailable_after' tag, you can tell Google that they should not crawl this page, after the promotion expires, among several other practical scenarios for this tag.