Note - We opted not to include vehicles that were rebadged within the same company, like the Ford Taurus and Mercury Sable. To be included, each pair of companies needed to be connected by an alliance, but one could not own the other.
Chrysler TC by Maserati (1989-1991)
The worst offender by far, the Chrysler TC by Maserati managed to sully the Italian allure of a great marque with common Chrysler hardware. Some question to this day whether or not Maserati has recovered from the TC. Some say it never will.
(Follow the jump for the final four and our Honorable Mentions)
Acura SLX (1996-1999)
The SUV craze caught Honda and its luxury division, Acura, off guard, so until they could develop SUVs of their own, each brand sold rebadged Isuzu trucks for a few years. The Honda Passport, essentially a rebadged Isuzu Rodeo, was bad, but not as bad as this Isuzu Trooper clone, the Acura SLX. Both vehicles have since been replaced by the Honda Pilot and Acura MD-X, respectively.
Chevy Nova (1985-1998)
The Chevy Nova winds up on this list for two reasons. 1) This tiny four-door economy car failed to fill the shoes of the original Nova and thereby sullied a decent nameplate, and 2) despite being a rebadged Toyota Corolla, the Nova still seemed to break down as often as every domestic econocar of the time.
Mitsubishi Precis (1990-1994)
Collaborating with new-kid-on-the-block Hyundai turned out to be a mistake for Mitsubishi, as the resulting product was the Precis. Mitsu hardly raised a finger to visually differentiate its Precis from the Hyundai Excel on which it was based. The only visual cue it's not an Excel is the lack of a Hyundai logo in the grille.
Toyota Cavalier (1995-200)
Some make fun of the lowly Cavalier, but Toyota thought enough of the third generation model to sell it in Japan for five years as the Toyota Cavalier. Besides being right-hand drive, it also had side markers, different taillights and a serious inferiority complex amongst its pure-bred Toyota brethren.
Dodge Challenger/Plymouth Sapparo
Chevy LUV truck
(We had fun putting this together, but know there are many more vehicles we all wish had never been born. Feel free to fill the comments with your own list of vehicles born from bad collaborations.)