I hate the assumption that all people who commit suicide are selfish. I do think that if you have someone who relies on you, like children, then it's horribly unfair on them and it perhaps is selfish to do something like that, especially if you're the only person the child has to rely on.
In most circumstances, I agree with anonymouse in that it's not selfish, you just want the pain to stop.
A close friend of mine was diagnosed with depression early this year and in March she took an overdose of her medication. She's fine now, and after it happened we got a lot closer from it, as it made her find out who her real friends were, but I could not help feeling incredibily guilty after I found out, because she told me about having depression, and I never kept in touch with her as much as I should have, although she said it was no-one's fault. After it happened she got the help she needed in terms of counselling and support, but I think it's sad that it got to that point before she got some help.
In the past I've had thoughts of doing something silly myself when things have gotten particularly bad, but I've never come to the point of doing anything, mainly because I was too frightened and knew how much it'd hurt my mum. Although I will admit that I've self harmed a few times, not in the intention to kill myself, but just to sort of release some of the emotions I had built up - something that I didn't even tell my counsellor, which I regret now.
I think suicide is a scary and deeply upsetting thing, but if someone genuinely wants to do it, they'll suceed, and the most upsetting thing of all is the amount of people that actually succeeded that could have been helped. I really think that there should be more support out there for people who are suicidal, the only thing I can think of is the Samaritans, but there really should be more out there. Like Legolas said, despiar is a terrible thing to go through alone.