I usually 3 or 4 box, but when i do 2 box, i go with...
war/sk
cleric(merc)
bard
cleric/rogue(merc)
(not a big fan of casters, specially as mercs, prefer melee and healers!!
on the new progression server i have been 2 boxing
Sk
Druid
(i know a shaman/cleric would be a better box, but its...