The rarest car I've ever seen, I guess, is a Tucker. (anyone seen the movie?) I don't have any pictures, but I do remember it. It had this little lever hanging off the steering column that had a conventional 4-sp manual pattern to it, but could be flicked with a finger or thumb. There was no dashboard (by design) on the passenger side, making the interior look HUGE.
This was about 1989. It was summertime and I was with my father in Michigan, who was on a business trip. We stumbled across a bunch of old cars owned by Domino's Pizza (which I think was HQ'd in Michigan at the time). They had everything from this Tucker to an Indy car that was used for special events.