I'm not a regular poster so flame away if you like. My friend was running my lvl 11 paladin through the deadmines using his 70 paladin to power lvl me. Well after run 4 we were getting a little bored so I was spamming holy light on him just to see those amazing 80 HP heals. He then cast the lvl 70 version of blessing of light on himself low and behold my level 11 paladin crit heal for 490 hp, meaning apparently blizzard never nerfed the +heal gained from blessing of light which with a little more experimentation we found out you gain the full affect from using down ranked versions of your heals with this blessing up thus saving mana for those long fights.
Another one we figured out was with the shaman totem that lowers the cost of your lightning bolt by 15 mana (can't remember the name I believe it's totem of the void) it makes your rank 1 lightning bolt cost 0 mana. Now why would a lvl 70 care if there rank 1 lightning bolt costs 0 mana you ask. well in those long fights against nightbane and gruul and people such as those you will run out of mana after awhile, well elemental shammies with this totem can just spam rank 1 to proc clearcasting and also if theres a judgement of wisdom on the target they regen mana at a very speedy rate.
and finally as a side note if you have a friend who is also a priest, you can time your power word shields if you cast at the exact same time to stack on a target.