Elephant.
It is about a shooting at a school and is loosely based on the Colombine (sp) massacrer. Most of the people in it are not actors, they were students or teachers at the school where it was filmed and there was little in the way of a script, just ideas.
Stunning, but has no hope that this won't happen again and again.
If you don't get on with slow films don't bother with this. You will hate it.