Well, lets see...
I really like the old "Bulletproof 3800", a GM V6 that comes in cars (like the Bonneville, for instance). Those engines will run to 300k before they start acting like they're tired, and you can usually get 400 out of them before you have to rebuild them.
That is, so long as you take care of them.
I'm fond of the 216 in my truck because even
I can work on it!
