Quote:
The 2008 American Silver Eagle is the obvious error that comes to mind. The 2008 coins changed to a different font, best identified by the "U" in United States on the obverse. Starting in 2008, the "U" should have a serif on the bottom right side. The error coins have the 2007 and earlier style of U.
Not really the question that was asked, but I wouldn't consider this one an error because the change was intentional.