Porsche 956/962 - the total number of wins, and the length of time over which it was a top racer make this, by far and away the top Porsche. It was fast, well balanced, and ran successfully in the midst of rules changes that forced fuel efficiency... and then was still fast enough the gain an overall win at Le Mans nearly 10 years after it's "prime." The engine still serves as the design base for the top of the line street cars as well (Turbo, GT2, GT3).
Porsche 917/30 - Even the 917 in general... these were outstanding cars that defined Porsche as a race winner, and started the real evolution of cars capable of overall wins (the 917 to the 936 to the 956 to the GT1). But the Penske evolution of the turbo Can Am car, the 917/30 deserves special mention. In a time of very fast cars, this car was SO much faster and so far ahead of it's time.
Porsche 911RS - the original RS of 1973 is still the standard for what a street going Porsche should be. With each new version of the GT3 or other top line car, the question that always comes up is "how does it compare to the RS." The RS certainly can not match the newer cars in terms of outright speed, though it is still quite quick even by modern standards. But the ideas that created this car (built and sold for less than it's cost for fear they wouldn't sell enough to homologate the RSR) is still the blueprint for similar Porsches. And the original is special.
Porsche 904 - Quite possibly the most beautiful Porsche ever. Mechanically, the 904 is very much an evolution of the earlier mid-engined cars (550, 718), but unlike those that would come later (906), this was still very much a usable street car.
Porsche 959 - Designed as a test bed for new technology and to run Group B Rally, it was a wild success with the former, while rules changes never allowed us to see how it might do with the later. The 959 was a technological powerhouse, and all these years later, it still can boost of the most advanced AWD system ever put into a car! Elements from this design leaked into all other Porsche designs over the next decade making this one of the most influential cars they've ever produced.
Porsche 1 - The first one! While the Gmund Coupes that followed were more direct ancestors to the 356 and later Porsches, the first car deserves mention as just that. While it proved impractical to produce at the time due to parts availability in post war Germany, the overall design and aim of the car would define many elements of Porsche street cars.
Porsche 930 - Not as aggressive as the 945 or Turbo RSRs that directly preceded it, it had the plus of being a true street car... and still having the 917 calipers (ie "Hand Of God" brakes). The intercooler versions were the best of this breed, but all the 930s were special cars. Similar in many ways to the RS, but where the RS would be elegant and carefully thought out, the 930 would go for simple brute force!
Carrera GT - While possibly lacking if compared to the 959 as a technological showcase, the Carrera GT will likely have a similar impact based on the number of design and manufacturing patents that came about as a result of it's production. Aside from that, it is a beautiful, elegant, and downright brutally powerful car. Everything one could want in a super car.
Porsche 908 - getting to the tail end of the list and still so many cars to consider... the 908 was so often an also ran as it often had to compete against the 917. And compared to the 917, it simply didn't have the power... but it did have an amazing power to weight ratio, and it's maneuverability on some circuits showed what could be done with less! Also, many of the design elements that would make later 917s so dominant, started life on various 908 versions... and while the 917 was more directly the ancestor of the later racing program, the 908 was very much the philosophical guide to those developments.
Porsche Junior - ok, so maybe this doesn't belong here! There's is the current RS Spyder that is beating LMP1 cars... or the 996GT3RSR that was so dominant in the GT Classes! Or what about the original 911? Or the GT2? Or even the much disliked Cayenne just for it's engineering achievements? Or the little known 914-8 as the "ultimate 914?" All worthy of this tenth spot, but instead, let's give it to the only tractor Porsche ever made!