Many of you probably already know these stories. Even I as a rookie getting back into the hobby knew about some of them. Still, an interesting little slide show: http://www.marketwatch.com/story/the-1-million-penny-and-7-more-famous-coins-2012-09-06
None are more famous than the 7 Million Dollar eleven cents piece. I'm surprised it hasn't been posted here yet.
I thought it was "worth" 11 and he turned down that very serious "7.5 million offer", didn't he? The mere mentioning of "Accugrade" or "double denomination" seems to being him out of the woodwork. Now just give it time...