You get the car you find. Like if you see a wreck of a VW Bug (Its Ibiza area 1 i think) if you find all 10 you'll get a VW bug to drive around in. Its pretty cool. If you go on Youtube and search you can see a video of all the locations and where they are. Thats how I found them all and its quick and easy.
Google Maps - that's brilliant Thanks so much for the links. I'll try to find some cars and take some photos while I wait for the new cheat for the updated game. This game is just to freaking hard to play without cheats