There exists heals such as Bleat which I think (please correct if I'm wrong) is one of the strongest single cast heal around. Then there is the Cleasing Rain which heals a bit and also changes the weather to boost all heals. Lastly, mechanical units have a heal similar to Bleat with the difference of slightly less healed amount and it only applies to other mechanical units in your team.
Wowpedia has listed most of all pet abilities and it also tells which pet has the heal in question. Here are few, probably more exist but they are likely "copies" of these spells:BleatCleasing RainInspiring SongRebuild