Tried a few duos, some as disc some as holy or some disc/holy mix:
Mage/priest: nice, as we like eachothers buffs and they'll love a disc priest's shield, disadvantage seemed to be 2 clothies together meant a little competition for nice drops.
Hunter/priest: let the pet tank, while the pair of you safely nuke away from a distance.
Warrior/priest and feral druid/priest: tanking class with priest makes for an unstoppable combo that can just keep going and going - whether that be mob after mob or on some 3/5-person group quest elite, the squishy priest takes no damage, the warrior/druid never has to stop as the priest can keep them up between damage spells, with the druid I love being able to say 'innervate please', 'lfg, need 3 dps' makes looking for pug groups easy and I can go in without the dread of finding a hopeless tank!
Never tried Shaman/priest, but have tried Enhancement shaman/mage: my shammy is suprisingly squishy and hopeless as some sort-of tank, mobs had an annoying tendancy to run after the mage every time they got a big crit, but in this case the mage out-geared my shaman, disc priest damage wouldn't be so bursty as a mage's, plus a disc priest could help keep up the shammy.
Edited, Feb 16th 2009 10:04am by Helluna