Jumping into an erupting volcano - surely you can't die if you actually succeed in jumping into the lava, and don't get saved by some large gust of wind that somehow blows a human back
up onto the ledge.
If there weren't so many people in one area, and you weren't allowed to have a relationship until after 18 and schools had maximum security measures (it seems we're heading that way anyway), then there would be no school shootings, unless they were very smart. (assuming the security is as well)
I don't think you will ever stop suicide.
On a side note, have there been stories of animal suicides? (beside the lemmings that run off cliff tops or whatever)
EDIT:
http://news.softpedia.com/news/Do-Animals-Commit-Suicide-63441.shtmlAnother issue: Lemmings do not commit suicide! Each 4 years there is a cyclic demographical boom of the lemmings (small arctic rodents) followed by a desperate massive migration during which many die throwing themselves into the rivers, lakes and sea.
It has been regarded as a collective suicide, conscious or involuntary, caused by over-population. In reality, being solitary rodents by nature, when the population booms, the stronger lemmings drive the weaker and younger ones off long before the food is depleted.
The young lemmings disperse in random directions looking for vacant territory. Geographical features constrain their movements and channel them into a relatively narrow corridor and large numbers can build up leading to social friction, distress and eventually a mass panic can follow and they flee in all directions, but they do not deliberately march into the sea; this is just pure fantasy.

Hopefully humans won't have to do this.