My best had to be last year when I stopped at the gas station on the corner by where I work. It was of course owned by a person of let's just say "foreign decent". When it was time for him to give me change back, he asked me if I wanted some silver dollars instead of bills. I guess the silver dollars didn't fit well in his cash drawer? Anyways, I was thinking he was going to give me some modern silver dollars, but when he handed them too me I could see they were old. I said "thanks" and headed out the door. Once outside I discovered that he had given me three silver dollars from the 1920's!!! Man, was I overjoyed. I went back to work and was talking to a few co-workers about the incident. Our receptionist said a similar thing had happened to her husband a few days earlier at a country store about 2 miles down the road. Apparently someone was either hard up enough to cash these in, or else someone was getting rid of stolen coins? All I know is I actually made a nice profit that day.
A Canadian nickel that sticks to a magnet. And this far south...strange. I did get a '64 quarter recently, but the novelty of the nickel beat it. I know, I'm weird...
I've never had anything special from pocket change. My wife, however, got a 1919 Wheat penny in change last year. I've always wandered how it made it to 2006. Maybe someone was hoarding it and accidentally spent it. Needless to say that penny is now out of circulation now.
A friend came to my office 2 years ago with a strange coin he got in change... an 1853 Seated dime! I was shocked, and he gave it to me, too. The front is dark, about Fine grade, and the back is completely slick. It looks like it was stuck to the floor in an old house, face down, and the back of the coin was totally worn off over the years.
I'd have to say one single Washington Silver Quarter 3 years ago. I kept trying to put it in a coca cola machine and it would keep getting rejected. I took a closer look and noticed it was a silver quarter. Unfortunately, I laid it on top of the fridge and never saw it again.