Here's a couple not mentioned:
Disturbing: The beginning of RoboCop (yes, I said RoboCop) where they slowly shoot him to death. One limb at a time. It doesn't get much more disturbing than that.
...that is, unless we want to dredge up the classic "Clockwork Orange". That, my friends, is disturbing on so many levels.
Heart-wrenching: Somewhere In Time, when he finds the penny. *gulp*
Also, the classic "Where the Red Fern Grows". Saw that at the budget theater when I was a kid and there was not a dry eye in the place as we left. Of course going from theater dark to a bright sunny summer day with white pavement didn't help, but there were sad tears there too.