A discussion in my class on this topic was sparked off by the recent news of the decision by a 104 year old Australian scientist, David Goodall, to opt for voluntary euthanasia.
Before learning Buddhism, I would say I was pretty neutral on how one should end his life - it is his own life after all.
However, I think the Buddhist teachings are quite clear on the preciousness of life.
This video by Master Sheng Yen will say it much better than I ever can:
Anyone else has their views on this?