Totem of wrath stacks 5x (so +15% crit and +15% hit, on top of the 11% crit from talents, 5% dps from lightning overload, and 5% damage from concussion)
Healing stream stacks 5x (pretty nice hot, it looks like... but you'll probably use 3x, and use 1x mana spring and 1x poison cleansing)
Wrath of air does not stack (+121 spelldamage)
Grounding "stacks", sort of
5x magma or firenova is pretty good AOE dps
5x searing sounds pretty good, but I haven't seen it used in Xbox's vids
None of the earth totems stack, but staggered tremors in a castsequence macro are basically fear immunity
Staggered bloodlusts for perma-haste, basically

That's pretty much it, I think.