I think euthanasia, as painful and as difficult as it may seem, is sometimes necessary. I don't really believe in an absolute morality that extends beyond an individual's own subjectivity, and so I could never say something was wrong or right for EVERYBODY without feeling horribly presumptuous.
Having said that however, it seems to me that the general consensus on the attitude towards the sanctity of life is somewhat... thoughtless. While I am not saying that people should go out killing others willy-nilly, I do believe you have to try and bear in mind the quality of life a person is experiencing when this issue comes up. A bubbly, happy existence that last only 20 years is better than a depressed miserable one that lasts 80.
Suicide in general... man, I feel like I'm going to catch some serious flak for this, but I'm going to put it out there anyway.
In my experience, there are two general ways a person can die. They can die from the death of the body, or they can die from the death of the mind. The latter being what we call suicide. And this attitude of "Whatever doesn't kill you, only makes you stronger" is NOT true. You cause enough psychological trauma, you WILL kill the mind. The mind dies, but can't fully do so without the body, so it takes the body with it. This is how I see suicide. I've lost people in my life to it, and to me, that's what happening. It's the death of the mind as a result of experiencing something more than it can actually handle. And as hard as it was for me to accept, it is their choice to make. Again, I could never make the moral judgment to say in any absolute sense that what they chose to do was either right or wrong. It is their life and their decision.
Similarly, when the body dies, the mind must be taken with it as well - I think this is what may be referred to in ESP or near-death experience circles as "limbo." There are some who believe that after a body dies, the entire person will not completely die until the mind has let go of its own existence. So, in essence, for a complete death to occur, both mind and body must die.
That's all I got.