I'm not talking the year ( 1970 ?) they left the S off of the dime ( maybe on purpose ?) type of stuff ! I'm talking like double struck, clipped planchet, cent on dime planchet, off center strike, type of stuff. Does anything like this exist ?
And a brockage. http://www.littletoncoin.com/webapp/wcs/stores/servlet/Product5|10001|24551|-1|36063|89312?nav=1 BTW, it's a sales site, but it's not mine. Sorry if that's against the rules.
The most dramatic proof error is probably a mid stage 1968 half dollar die cap that was pounded into a proof set and shipped normally even though the case didn't close. There were a lot of pranks with mint and proof sets in those days.
I've seen pictures of a 1973-S proof Ike struck through a dime planchet. Ike's head was perfectly centered on the dime blank. Then there was the 1970-S quarter struck on a 1900 barber quarter. Not really an error because I'm sure it had help. In fact both of those probably had help. When I worked in a shop I had a customer bring back a "defective" 1968 proof set I had sold him the day before. I hadn't paid any attention to it because who pays attention to 1968 proof sets. Well the quarter had about a 15% clipped planchet. I told him I would be VERY happy to take the set back and exchange it for another one, but that the error quarter in the set was worth a LOT more than what he had paid for the set and that I would be happy to BUY the set back from him.