A while back, I found a strange penny with a face that someone stamped on it and some sort of glue material on the 'tails' side of the coin. After a bit of internet searching, I found some references to a penny that was stamped with John F. Kennedy's face on it (facing Lincoln's). After guessing that it could possibly be Kennedy, I found some information about it. Unfortunately, the coin itself is rather worthless, but kind of an interesting anectdote to history, anyway. Personally, I was hoping for some sort of weird conspiracy. Ah well.
Here is the best information that I found about this coin.