A very touchy subject and one which I think naturally brings out strongly differing views precisely because, in my humble understanding, this is one of those issues that should be treated on a case-by-case basis rather than trying to find a blanket answer for the issue as a whole. As Dr. Sahib and others have pointed out before, Allah did not forget to place in the Qur'an whatever we do not find there. Some of it, like the issue of rape not being explicitly mentioned, as if to say that we shouldn't need to have the horrendously destructive nature of the crime explicitly written down for us, is about common sense (i.e. the type that involves actual reasoning). Other places, it is about leaving for us a timeless framework, the specifics of which can change with time through by-laws (again, through the application of reason).
In the case of suicide, I think it is one of those things that it is relatively easy for us, especially those of us who are relatively well off, to say that it appears on the surface to be a lack of respect to the God-given responsibility to our actions and dependents, and dignity to our Selves. But I find that in many cases (though not necessarily all cases - this being precisely the point) when I actually read the details of the life that the person in question had to endure, I find myself wondering: it's easy for me to pass judgement staring through my monitor, but how would I really have handled life if I had to walk in this person's shoes? And then suddenly the grays of the issue seep through and I find a black and white decision difficult to reach.
There are many different reasons why someone decides to kill themselves, some ideological (think Kamikaze, suicide bombers), some fantasy brainwashing (again, suicide bombers), some extreme hardship caused by others, some extreme hardship caused by ourselves, as well as a variety of disparate issues like being in a vegetative state (Dr. Shabbir has discussed euthanasia before), or even having acid thrown on your face if you're a poor women in Pakistan apparently.
I believe there is a verse that speaks of how there are those that are in the middle: they have done both good and bad deeds and the issue for them is not clear (sorry but I can't find the verse in question). In this case God will decide between these people, where any of us passing judgement could not clearly know one way or the other. The point is that let's not be quick to pass judgement.
I don't often do this, but here's a quote from Einstein (a paraphrase of a quote actually): Everything should be made as simple as possible, but no simpler. All these different situations and experiences bring with them an incalculable complexity that leaves us with the only seemingly reasonable response: to treat all suicides as a singular matter and in turn to ignore the life story that leads one to take this ultimate decision. If a judge in a truly Islamic state was unfortunate enough to have to deliberate on a suicide case, I would hope this complexity and the person's life story is carefully and compassionately considered.