The cars you are looking for generally fall into two camps: Cars that were rare or limited when they were orginally built (step forward Lotus Carlton and Escort Cosworth) and mass produced cars that the public take to their hearts for some reason (VW camper/beetle, Fiat 500, mini etc). The first type are usually fairly easy to spot as long as the manufacturer doesn't ruin it by deciding to release more (Clio Williams anyone?). The second group are much more difficult to spot early on, which is why I'm going to leave it there 
