Well, my wife's 1995 Neon has around 135,000 on it. But it's not the original engine (as some of you are testament to.
My 1986 Toyota has 196,000 all original miles on it.
But my current champion is my old rusty but trusty truck. 336,000 miles on the original engine and only a minor rebuild on the tranny. When we had our little nippy weather session last week, it was the only one out of all four vehicles in my driveway that would start (with a little help from 30 minutes on the block heater of course.....).
As for previously owned, I think I'll topple the forum with my old Toyota pickup I had in Washington state. 705,000 miles when I got it, and at last I heard it was still going strong as it rolled over 800,000. The number plate is still current, so someone's still driving it somewhere.
As for the most miles I've put on a vehicle would have to be my little sleeper 1979 Chevy L.U.V. 4X4 pickup truck. I put 112,000 miles on that myself. I can also lay claim to 150,000 put on one car, but it wasn't mine. It was a 1980 Dodge Aries station wagon that belonged to the taxi company I drove for.