That car you saw at the end of The Avengers? It was actually made in 1992 and had more than 250,000 miles on it. 

That's right. The slick, beautiful concept convertible that Robert Downey Jr.'s Tony Stark and Mark Ruffalo's Bruce Banner peel off in during the final scene was a twenty year old car.

Joss Whedon, the movie's director, gave Acura designer Dave Marek three months to get him a working car for the final shot. Marek decided it was going to be an Acura NSX, the same car from the Superbowl commercial with Jerry Seinfeld and Jay Leno. The Superbowl commercial was still month's away, though, and the company hadn't announced they were relaunching the NSX yet. So they did an Avengers-specific design of the car and contracted a company to build it for them. 

But instead of building the whole car from the ground up, they took an old 1992 Acura NSX and built the rest of the car around it:

Underneath the sleek body panels of the NSX film car sits an original, fully-functional 1992 Acura NSX with more than 250,000 miles on it.

TFX simply stripped the original NSX of all its body panels, save for the doors, and built the concept NSX around it. The front panels are made from fiberglass while the rear panels are milled epoxy resin. Cladding was added to the doors so they matched the look of the rest of the car.

They replace the seats in the car, too, but otherwise everything else stayed the same. The car can't even go over 20 mph or its new frame shakes. This is what the final design for the NSX looks like, the one that was launched at the Detroit Auto Show in January (image via AP):