Here are a few thoughts. I've chosen them for significance as well as just looks and speed, passing up cars that were stupendous in appearance or performance or both but whose influence was something of a dead end. The list is not meant to be inclusive even for that year; there are of course many other good candidates; these are just ones that mean something to me. The years are those of US introduction.
1941: Willys-Overland MA/MB quarter-ton scout car. The world knows it as the Jeep.
1961: Ford Thunderbird. The first of the three years of these sleek and visually clean 'Bullet Birds' came during a period in Detroit history when a lot of car companies were evolving from the tailfin era with a sort of awkward angularity.
1963: Porsche 911. The internals have changed greatly (and the visuals somewhat) over the years, but they'll still be making that same basic shape when the powertrain consists of Cochrane nacelles and dilithium crystals.
1964 1/2: What else could that one be but the Ford Mustang. Most great machines are evolved over a period of time. This one sprang full-grown from the forehead of Athena (well, that sounds better than 'born of a Ford Falcon and midwifed by Lee Iacocca,' but you get the idea).
1963: Lotus Elan. A perfect little haiku of a car in which not a line, a pound, or an inch was superfluous.
1967: BMW 1600. Before long it grew into the 2002 series. Word got around. By the time their next generation of small cars was introduced, a company once obscure in the US was poised to become a standard outfitter of the newly minted B-school graduate.
1970: Datsun 240Z. An E-Jag for the masses, and the beginning in earnest of Nissan's previously modest entry into the US market.
1975: Chrysler Cordoba. Loved the commercials with Ricardo Montalban digging his fingers into the leather seats and hissing, 'Revenge is a dish that is best served cold'... Oh. Sorry. Wrong show.
1976: With gas prices getting painful, Honda comes to the US with a car that Americans considered reasonably sized, which was nonetheless highly efficient by our standards, and the rest is history that's still being made.
1980: AMC Eagle. Here is the lineal technical and corporate antecedent in the American market for the idea that a fairly luxurious vehicle with unibody construction and an on-road 4WD system was a reasonable thing to build, and thus the XJ-chassis Jeep Cherokee of 1984 and thence (for better or worse) the blanketing of the American road with sport-utility vehicles.
1984: Thunderbird again, this time in the vanguard of Ford's 'jellybean' aerodynamic era that would soon produce the hugely popular Taurus.
1986: Acura Legend. A nice car in its own right and also a business pathfinder as Honda expands its frontiers (and charts the way for Toyopta and Nissan) by hiving off a new upmarket division.