Unlike the store-brand boxer briefs I am currently wearing, that offers room in the front for coconut-sized balls, but allows for no extra padding on the back side(I'm not that fat dammit), a few cars, every now and then, get the proportions and design elements just right and achieve the status as "timeless designs".
Their designs differ from their peers'. Perhaps wonky even, seen through contemporary eyes, but the future worked in their favor, their design cues became a standard. They got it right.
It is hard to tell which of the cars of today will truly become design milestones, and which will become the next Aztec. Or maybe, ten years from now, we will look back at the Aztec and consider it ahead of it's time.
Here's a few cars off the top of my head. It's probably very euro-centric and far from complete! Feel free to contribute more/shoot my suggestions down.
1993 Toyota Supra mark IV
Going on sale in 1993, sporting clean, flowing lines, exiting proportions and big, characterful headlamps. These cars looks as natural on a racetrack or in a showroom today as it ever did. Hopefully a kind soul with a good heart will keep one of these in stock condition for our children to witness.
1996 Lotus Elise
Blending classic British roadsterisms with a unique new design language, the Elise is still inspiring, and often lending parts and platforms, to a lot of the sport cars of today. True, much of this is due to Series 2, but I still think this car belongs of the list for planting a seed that you can find in everything from the game changing Tesla Roadster to the record breaking Hennessey Venom GT .
1996 Volkswagen Passat
It was the mid nineties. The people demanded soft, sweeping curves, large surfaces and aerodynamic everythings. While most car designers were dropping blocks of marzipan from the ceiling to attain these naturally rounded shapes(see Taurus), Volkswagen understood that a little restraint goes a long way towards a successful design. It might seem unimpressive, nay, boring, but a quick glance at VAG's modern line-up reveals just how well this design language stands up to the test of time. I considered putting the 1994's Audi A4 in it's place, but frankly, I think the Passat ages more gracefully.
1996 Ferrari 550
Finally doing away with pop-up headlights and the large, flat surfaces of yesteryear, Ferrari played on all the right strings with the 550. Perhaps not the most impressive or important of the Ferraris of the nineties; It is, however, arguably, the hardest to date.
1993 SRT Viper
Is it a Dodge? Is it an SRT? Isn't SRT a part of Dodge? Who knows. I don't. It just works. Shut up.
1997 Peugeot 406 Coupé
The front of this car hasn't aged perfectly, but the rest of the car sure has. "Gorgeous" is a word that comes to mind.
1994 BMW E38
Perhaps not as future-proof as the other cars I've chosen, but with a nearly unlimited supply of class and restraint, this car's cool chills my bones to this very day.
1999 Honda S2000
A small, well handling roadster with an extremely advanced N/A 2.0l four-banger producing 240hp at a screaming 8300rpm. It is easy to see why it is often overlooked ... no, wait it isn't!