Spell and racial regen, bear form, and fungi
 

Anyone have any further detail or info on how/if these stack?

They should all stack together.

15 - Regrowth
15 - Fungi
18/12 - Level 60 Iksar Regen
2 - Bear Form

On top of that, Auras of Battle should stack (I believe this is bugged on P99):

2 - (Feet) Boots of Silent Striding (Dozekar Quest)
2 - (Waist) Belt of Dwarfslaying (Dain Head Quest)
2 - (Wrist) Spirit Wracked Cord (Chardok Quest)

So the theoretical maximum regen for a 60 shaman is 56 HP/tick sitting or 50 HP/tick standing.

Fungi still has value even with torpor when you look at that potential. Too many throw theirs out cause Vindi BP offer 2 regen IMO.

That combo is pretty much a canni/mana battery even at 55/bear form obtained

Troll/Iksar racial:
12 sitting, 8 feigned, 6 standing

Bear Form: Increase Hitpoints by 2 per tick

mana dependent Regen

39- Chloroplast: Increase Hitpoints by 10 per tick
52- Regrowth: Increase Hitpoints by 15 per tick

Fungi Tunic: Increase Hitpoints by 15 per tick (L20)