636K miles, '92 Chevy Astro van.
No work done on engine or transmission. Only stuff like altenator, waterpump, balljoints replaced.
Drove 120 miles round trip every weekday for several years. Long trips help the engine dry out and warm up properly, leading to better engine life. Oil changes every 3k miles at home, Quaker State 30 weight. When we finally started tearing the engine down after it started giving us major trouble, it was clean as a whistle inside.
Many people think that anything over 100K is high mileage. It isn't. We don't have the money to trade in cars every couple of years for the latest model, so we drive 'em a long time. Last cars we bought were my father's '99 Suburban with 130K miles on it, and my '99 Silverado with 110K miles on it.