Mk. I Volkswagen GTI - It was one of the first notable hatchbacks that had truly astonishing performance for it's size and type, and is credited with creating the "hot-hatch" segment that many of us know well and love today.
Mercedes 190E 2.3-16 - While everyone knows the more famous 190E 2.5-16 Evo II, the 2.3 represented the first great Group A homologation special created for the series that ignited a spark in BMW which caused them to create the, now legendary, M3. The Evo II would also make a great premium model.
BMW E30 M3 - Created in response to Mercedes' domination of Group A (albeit unofficially, as Mercedes was not supporting factory racing efforts at the time), the M3 needs no further explanation for it's greatness, as it went on to become one of the finest performance and racing cars ever made.
Toyota 2000GT - Easily one of Japan's first great sports cars to be recognized on an international level. The 2000GT combined an innovative engine with a gorgeous exterior design.
Toyota Celica ST185 GT4 - It wasn't the first Japanese WRC rally car, and it wasn't the first rally car to use a turbo-charged 2.0 liter engine with All Wheel Drive... but it was the first Japanese car to be successful in the popular Group A format. The ST185 won several WRC championships and made awesome homologation specials like the GT4 (relatively) popular years before Mitsubishi's Evo and Subaru's WRX STI were popular.
Plymouth Superbird - A record-breaking NASCAR at the time, the aerodynamically optimized Superbird dominated the single season it ran, being banned the next year due to its performance. It is still one of the most unique and notable vehicles to come out of the muscle car era. (Alt: Dodge Charger Daytona)
Buick GNX - One of the fastest cars of the Malaise era, the already powerful Grand National was transformed into the limited and mighty GNX with help from McLaren. It's Turbo V6 made it faster than the Corvette's of the day (as it's "underrated" performance numbers were only 5hp less than the '87 Vette's V8).
Rondeau M379B - Not a car you've heard of, but it is historically significant as it is the only car to have ever won Le Mans outright while being driven by it's designer, Jean Rondeau. To this day, this is the only time this achievement has every been accomplished.
Mclaren F1 GTR - A car that wasn't supposed to be a racecar that ended up winning Le Mans outright. The F1 GTR showed the true potential of Gordon Murray's design that would later be extended by the long-tailed versions (although they would never match the success of the '95 GTR's win at Le Mans). This car also marked the first time a racing driver of Japanese nationality reached the top step at Le Mans, with Seiji Ara being the only other to follow in 2004 with Audi Sport Japan Team Goh's win.
That's all I've got for now...