I'm wagering these 2 combo will be the scariest you can find.
ret has 1 min repentance
potential 30 sec CD HoJ
enh has 30 sec hex
ret has CS, divine storm, JoC, SoC proc, HoW
enh has storm strike + ES, windfury weap
general white dmg from both class
ret has ret aura that benefits shammy as well
shammy has lightning shield
ret has sacred shield, DS, DP, HoP, plate
shammy has mail. Can get the benefit from pally
shammy has frost shock (also deals dmg), and earthbind totem
ret has JoJ for slowing druid's travel form
grounding totem, earth shock (spell interrupt)
BoM, WINDFURY TOTEM, mana spring, JoW, HEROISM
pally/shammy general healing spells + divine storm
PURGE + CLEANSE. yes. you take out priests like slicing butter with a hot knive.
I can't think of another class that will give more synergy than a shammy. MS war is good, but they can be rage starved, lack CC and depend heavily on pally's HoF, while shammy can break movement impair with ghost wolf.
The only thing unknown is ret + DK.