Is there any documented evidence for suicide among vertebrates other than humans?
Well, there are certain behaviors that may qualify. The clearest example I know of would be sexual cannibalism, and more specifically (source):


  The redback spider is one of only two animals to date where the male
  has been found to actively assist the female in sexual cannibalism. In
  the process of mating, the much smaller male somersaults to place his
  abdomen over the female's mouthparts. In about two of three cases, the
  female fully consumes the male while mating continues. Males which are
  not eaten die of their injuries soon after mating.


That sounds pretty suicidal to me...

A less flagrant but commoner example is that of mothers dying to nourish their offspring. Again often seen in spiders, the best example I know of is the giant pacific octopus (Enteroctopus dofleini). The female will chose a den and lay her eggs. She will then spend her last weeks tending her young, never leaving the lair to hunt. Eventually she dies of hunger and her body nourishes her young. My source here is the wonderful BBC life documentary series. 

Neither of these are vertebrates of course but still, I thought the suicidal little spider was interesting.