Suicide.. sin or quiet silent death?

When one thinks of suicide in todays society you think of someone with a psychological problem. Or if you are a christian you look upon suicide as an offense towards God. Thomas Aquinas, for insistence, believed that suicide went against the natural law of self preservation, and it went against God's view of life and death. In the Inferno, circle 7, Dante writes about a dark forest. In this wood are trees with thorns, and in order for Dante to hear what the trees have to say he must break a piece of of them, causing them pain. Only through the pain can they express themselves. This is a reflexion to the pain they felt in life and their answer, self mutilation. 

But not all suicides are in this wood. The more important ones such as Dido are reserved for another circle. Does this mean that that there are excepted suicides? Throughout history you see many great men choose suicide over another fate, such as Socrates. But you also see many terribly disturbed people commit suicide. In 2005 is suicide was 11th ranking cause of death and more people killed themselves than were killed by others. There are many reasons for suicide such as unrequited love, guilt, grief, self sacrifice. Obviously our society is not full of people killing themselves for something they believe in. 

 The main question I want to ask is.. could there be a good reason for suicide? Could there ever be an instance where it is necessary or the right course of action?