Suicide is, in effect, self-murder. The unfortunate thing about it is that the one who commits it cannot repent of it. The damage is permanently done. We can see in the Bible that murderers have been redeemed (Moses, David, etc.), but they had opportunities to confess their sins and repent. With suicide, the person does not. But that does not mean the person is lost. Jesus bore all that person's sins, including suicide. If Jesus bore that person's sins on the cross 2000 years ago, and if suicide was not covered, then the Christian was never saved in the first place and the one sin of suicide is able to undo the entire work of the cross of Christ. This cannot be. Jesus either saves completely or he does not.
That I cannot answer because I cannot list every possible situation. But, it seems obvious that suicide is clearly wrong, though forgivable. However, there are general categories of suicide that we could briefly comment on:
Medically Assisted Suicide - I've never seen this as being acceptable. The doctor is supposed to save life, not destroy it. But, lately as destroying the lives of the unborn is more common place, destroying the lives of the sick has become the next logical step.
Suicide to prevent prolonged torture - Let's say that someone was being tortured in an excruciating manner for an unbearably long period of time, is suicide an option? Perhaps. But if it were in this situation, why wouldn't it be all right in the medically assisted context if the patient were also in excruciating pain for long periods of time? Quite honestly, I'm not sure how to answer that one.
Suicide due to depression - Of course, this is never a good reason for suicide. Seasons pass and so does depression. The one who is depressed needs to look to Jesus and get help. Depression is real and powerful and is best fought with help. Also, severe depression robs the mind of clear thinking. People in such states are in a real way, not in their right mind.
Suicide due to a chemical imbalance in the brain - The human brain is incredibly complex and the medical community is full of accounts of extraordinary behaviors by people whose "circuits got crossed." I don't see how a situation like this would make it justifiable. I think it simply would make it more explainable.
Accidental suicide - Sometimes people accidentally kill themselves. This could mean leaning over a balcony too far and falling to one's death, or actually, purposefully taking a stupid risk like playing with a gun. Of course, with either, stupidity does not remove us from the grace of God. But then again, if it was an accident, it wouldn't be suicide would it?