These answers are mostly nonsense. The stability of a molecule tells you nothing about the intermolecular forces between molecules that determine the boiling point. I'm not sure why internal alkynes boil higher than terminal alkynes - you'd expect the polarity of the bond to the acetylenic hydrogen to make terminal alkynes boil HIGHER. But in any case, the answers that claim it has something to do with the stability of the pi bonds are wrong.
On the other hand, I can tell you that water boils higher than ammonia because the molecular dipole is much higher, for two reasons. The first is that oxygen is more electronegative than nitrogen, so the bond polarities in water are greater than those in ammonia and we would predict a higher molecular dipole as a result.
But the molecular dipole of ammonia is even less than we would expect for another reason. Imagine ammonia with the molecule sitting on a table with the lone pair pointing straight up. This molecule will spontaneously invert itself: keep the nitrogen in place and imagine the hydrogens popping up above it and the lone pair dropping down until it points straight down from the nitrogen. The molecule has inverted like an umbrella in a strong wind. (This is much like the Walden inversion of the SN2 reaction). Because of this inversion, and because it happens very, very rapidly, the ammonia molecule doesn't have a dipole moment - it points equally in opposite directions in the two forms, which average out.
This doesn't happen with water, which always has the bent geometry, and a permanent dipole pointing through the oxygen. Thus water boils a lot higher than ammonia.
( While both water and ammonia form hydrogen bonds, pure water has an equal number of hydrogen donors - i.e. hydrogens - and acceptors - i.e. lone pairs. Ammonia has only one acceptor for every three donors. I don't know if or how much this affects the boiling point, but it wouldn't surprise me if this fact were also part of the answer.)
