Final Exit is the closest to PPH. Most others are studies done on the hows and whys of suicide. Some I've enjoyed are:
* Night Falls Fast-Kay Redfield Jamieson
* The Suicidal Mind-Edwin S. Shneidman
* Why People Die by Suicide-Thomas Joiner
They vary in tone, keep in mind most authors on the subject will be pro life, though it's interesting to read their analysis of the topic.