You can use shaman/monk, but rather than a cleric for the 3rd toon I'd go for something more dps-oriented. You can use mercs for major healing, and the shaman will be fine for spot healing when the mercs go retarded. With the shaman I'd go for another melee class... rogue or zerker. Ranger might not be bad either, but that would be for buffs/utility + dps, with the understanding that the dps output of the ranger isn't going to be quite up to par with that of the rogue or zerker. On the other hand, all the jolt-type procs/abilities of the ranger would help with agro management, and he could also be a fairly decent tank should the monk bite it.