iCalendar: http://www.ietf.org/rfc/rfc2445.txt

Micro-Formated HTML: http://microformats.org/wiki/hcalendar

Rich Snippets

If Google understands the content on your pages, we can create rich snippets—detailed information intended to help users with specific queries. For example, the snippet for a restaurant might show the average review and price range; the snippet for a recipe page might show the total preparation time, a photo, and the recipe’s review rating; and the snippet for a music album could list songs along with a link to play each song. These rich snippets help users recognize when your site is relevant to their search, and may result in more clicks to your pages.

You can help Google surface this relevant information by adding additional HTML markup to your pages. This markup helps Google recognize certain types of data and display it usefully in rich snippets

http://support.google.com/webmasters/bin/answer.py?hl=en&answer=99170&topic=21997&ctx=topic

Event Micro format: http://support.google.com/webmasters/bin/answer.py?hl=en&answer=164506