Depends on what you call a close encounter, really...
I can think of a few times in the road car where I've avoided a big crash, but I don't really consider them to be close calls. I mean, every single time you pass a car on the highway you could argue that it is a close call - if either car was a few feet to its right and you'd have a big crash...
That said, the times that have made me appreciate my own mortality:
Big long, unintended front wheelie on the DT250, 1991-ish.
Spinning my road car completely unexpectedly, 2002 (not that I was in any danger of death, but it really wasa big wake-up call).
Canberra bushfires 2003.
Princes Hwy, north of Ulladulla, 2003
Nearly into the trees at ~140kph in the rally car, 2007.
Funnily enough, the actual crashes (rally car, road car, dirt bike, pushbike) haven't been the wake-up calls like the above list.