For me it has to be the original Audi U-R Quattro
Not only did I own one (once - it was silver), but to me it completely sums up the 1980's and the whole "performance, quality, and if it's expensive then so much the better 'cos I can afford it" philosophy.
Also, this IS the car that took 4-wheel drive out of the farmyard and onto the streets. I would argue that ANY high performance car with 4X4 (so almost all of them) can trace their lineage (and owe a debt) to the Quattro.
Mike.