Similar to many topics in philosophy, there are multiple views on the subject of suicide. I included several different view points, but I'm sure there's still a lot of information out there!

Discussion about the topic of suicide from a philosophical point of view dates back to at least the time of Plato. Socrates expresses his agreement with the thesis that suicide is always wrong because it represents the releasing of our souls from our bodies that the gods have placed us in as a form of punishment in Phaedo. Plato also believed the act of killing oneself is wrong, which he expressed in the Laws. Though he did define four exceptions: (1) when one's mind is morally corrupted and one's character can therefore not be salvaged (Laws IX 854a3-5), (2) when the self-killing is done by judicial order, as in the case of Socrates, (3) when the self-killing is compelled by extreme and unavoidable personal misfortune, and (4) when the self-killing results from shame at having participated in grossly unjust actions. (Laws IX 873c-d) (http://plato.stanford.edu/entries/suicide/). Plato considered suicide under any other circumstances due to one's laziness and cowardliness to deal with life's difficulties. Aristotle also saw suicide as immoral and hurtful to the state, but does not detail how it is wronging the state.

On the other hand, the Stoics did not see suicide as immoral. They believed if the means of living a naturally prosperous life were unavailable, then killing oneself maybe justified. Stoics believe that a wise person realizes that if advantages, such as good physical health, are lacking, then ending one's life does not affect one's moral virtue negatively or positively.

Christian doctrine generally believes the act of killing oneself is morally wrong. St. Augustine is credited with being the first to justify the Christian prohibition of suicide. He interpreted ‘thou shall not kill’ from the fifth commandment to include the killing of oneself. St. Augustine determined that suicide was an unrepentable sin. St. Thomas Aquinas later defended this position with the following justifications: (1) Suicide is contrary to natural self-love, whose aim is to preserve us. (2) Suicide injures the community of which an individual is a part. (3) Suicide violates our duty to God because God has given us life as a gift and in taking our lives we violate His right to determine the duration of our earthly existence (Aquinas 1271, part II, Q64, A5).

In 1783 David Hume wrote an essay titled “On Suicide,” in which he argues against the Thomistic position on suicide. The main arguments of Hume’s essay are: (1) If ‘divine order’ refers to the casual laws created by God, then it would always be wrong to break these laws in order to increase our happiness, but God often lets us go against these laws when we respond to illness or injury. (2) If ‘divine order’ means the natural laws God has willed for us that were meant to produce our happiness, then why should suicide be excluded from conforming to these laws if we feel the balance of our happiness is best served by it? (3) If ‘divine order’ refers to any occurrence that God has consented to, then God must consent to all our actions since an omnipotent God can presumably intervene at any point. If God has placed us upon the Earth like a “sentinel,” then our choice to leave this post must be acceptable by God.

From (http://plato.stanford.edu/entries/suicide/).

A helpful link if you're interested in reading more on the philosophical views on suicide:
http://comp.uark.edu/~mpianal/suicide.htm