Google +1 is a social feature for Google’s search service adding a one-click button to allow users to recommend sites and share those recommendations with their friends.
Appearing as a small icon next to each search result and text ad, logged-in users can share their recommendations with contacts through their Gmail address book, Google Reader and Buzz contacts and, eventually, Twitter contacts.
Download and info: http://wordpress.org/extend/plugins/google-plus-one-widget/