mine is a rare BMW 2002 tii turbo (unsure of the colour but it looked lime green!) - it was sat on a driveway for a number of years and i drove past it a few times, i kept meaning to go and knock on the door to find out what the story was.
i only knew it was a turbo as i was chatting to a old mechanic mate and he done some work on it years earlier
anyway, the day i go to find out about it the car had gone and the house also demolished

that's the one that i regret the most, i may never have ended up with it but its one i always wonder "what if"
what's yours?