Lost All Hope has a library of information on methods to commit suicide, including dangers of individual methods and their reliability, and statistical information on which methods are most successful.
In researching this site I was struck by how much has been written on suicide methods. Numerous bulletin boards with long discussions over different methods (often by people who had tried various methods of poisoning and failed), books and websites. I found it strange that there was so much discussion, in the face of very easy to obtain statistics on the most sure-fire ways of committing suicide.
The holy grail seems to be painless methods of suicide, and people will go to great lengths to find a method that might achieve that. The perversity being that huge numbers of these attempts end up unsuccessful, as the clean, relatively painless methods are often not done in such a way so as to make them lethal. And many of these people end up in hospital requiring treatment for their failed attempt.
The figures presented in the section Suicide statistics would indicate that for every successful suicide attempt, there are 33 unsuccessful ones. For drug overdoses, the ratio is around 40 to 1. In fact, if attempting suicide, there is a much greater chance you'll end up in hospital alive, with either short or long term heath implications, than dead.
So if you are reading this more worried about finding a pain free method than an effective method, you'd be well advised to read carefully the information on the dangers of the suicide methods mentioned on this site, then perhaps look at Help me, because you are much more likely to hurt yourself by attempting suicide than to succeed killing yourself.
For anyone committed to killing themselves, achieving the goal can be straightforward if a reliable method is chosen. The major problems are often not with the logistics, but rather the internal self analysis, and thoughts of how others will react (our behaviour is affected by how we think others will react). For many people contemplating suicide, they have a real desire to end their lives, but it is the fear of what their death might feel like that keeps them from doing it.