for those of you who would like to know what stacks with what here's a little info.
druids and rangers' get skin type buffs. several at higher lvl include hp and mana regen. druid's 60 something protection of the nine is one that has both hp and mana. same with their steeloak buff but it's just better. ranger's have pretty good group atk buff spells after 56, that stack with mostly everyone's buffs. mark of predator, call of predator, strength of tunare, spirit of predator, strength of the hunter, howl of the predator.
now to get a cleric or paladin buff to stack you'll have to get their symbol's buff. there are many levels or teirs' of their symbol's. more than likely tell them your lvl and they'll give you what's appropriate. whether it be symbol of kazad for those under 61, but over 46 or so. or if your 61 or over you'll get balikor or the increased on which i'm not sure what it's called. Paladin's get a nice hp+atk buff line.
now that being said the symbol buffs don't increase your AC. they only increase HP. so your not getting the added bonus from temp, virtue, conviction, or tenacity of having a higher AC.
now in addition to the druid and or cleric buffs. there's shaman and or beastlord buffs. that almost always stack with cleric buffs. beastlords get a very nice HP and Mana regen line of buffs, along with a hp+atk buff line too (i think) (look up spiritual brawn under beastlord)
later,
Hodra