I found a 1729 English half penny in not too bad shape. It's probably one of the first coins they had around here, and I consider myself to be pretty lucky to have found one. I found another in the foreign coins bin a couple of years ago.
My favourite junk box find was back when I was a teenager I found a 1788 Connecticut cent in a junk box - of course it was beaten nearly to death - but the dealer said he salted the box with it like 20 years before and it had been in there that whole time until I picked it out and figured out what it was. English halfpennies are a cool find though, they could have circulated in colonial America.