Something relatively painless? I have realized that it's actually quite difficult to kill yourself for certain if you try to make it painless, though--and even if you DON'T make it painless, because for all its squishiness, the human body can sometimes be shockingly resilient. Overdosing on sleeping pills just makes you sleep for a really long time, and it also gives people who find you the opportunity to rush you to the hospital, which really only makes your life MORE miserable because then you're saddled with bills you can't pay and mandatory psych visits you don't want. So I've thought it might be a good idea to combine methods, e.g. taking sleeping pills, and when you're about to nod off, tie a plastic bag around your head. You suffocate to death and you don't even realize it.