From Will and Ariel Durant's The Story of Civilization: Our Oriental Heritage... "One of his disciples concluded that Buddha would approve of suicide, but Buddha reproved him; suicide would be useless, since the soul, unpurified, would be reborn in other incarnations until it achieved complete forgetfulness of self." What is the primary source of this story? On a side note, what do historians think of Will Durant?
The Buddhist precept about refraining from killing is an important one and suicide is viewed in the same light as homicide.
Here's a very exhaustive list (caution: opens a PDF) of all suttas - our best primary source - that talk about suicide and as you will see, the outlook ranges from "strongly disapproved" to "condoned only under special circumstances".