Keeping to passenger vehicles:
Gas-engined: 1979 Dodge Challenger (really a captive-import Mitsubishi Sapporo). Somewhere just over 480,000 on the original engine, gearbox, driveshaft, and rear axle before it was perma-towed for unpaid tickets. My grandfather bought it new and it was eventually passed down to one of my cousins (she who accumulated the tickets). Some stuff (A/C, window switches) didn't work, but it was mechanically-unbreakable.
Diesel: Peugeot 504 with a reputed 1.1 million. Believeable from the condition of the car, but, amazingly, pretty much everything apart from the heated rear window was operating.