I found this game last year and boy was it awesome!
So basically its a driving simulator (freeware) that hosts tones of cars, trucks and planes, and has the best crash physics i have ever seen in a game. if you hit a pole, the pole will leave a mark in your car......pole shaped! With slow-motion feature and the game being freeware, it makes this a keeper!
http://www.rigsofrods.com/
Check out destruction of cars on you tube as-well.