Wanting a 3 box...i know shaman is the logical third box here but was contemplating a cleric instead...so besides the obvious of a shaman what are some other ideas on a third box willing to try a new class.
I would just like to let you know that the SK will require tremendous amounts of AA, Augs, and gear to be remotely efficient. Mine is currently level 85. Their damage is not really what you would expect however they are an awesome class. Since you can use the bard to slow, pull, etc, I would recommend adding a Berserker, Monk, Beastlord or Rogue. You will seriously be lacking DPS if you just go with a Shaman straight out of the box.
Well the plan is to run with three sizzle metrics...bard adds about 50% to each so I should have dps covered.
To take down tough names with a lot of HP's you need tanking, healing and dps and right now you lack both dps and healing. If you are going to add just one more box, then go with a good dps class, either a mag or necro or wizard, all three with advantages and weaknesses compared to the other.
I currently go bard/sk/cleric and there is nothing I can't do with that trio...but I have a TON of aa's. Also...at level 100 wizard mercs are ridiculous and will out parse most box toons in non-raid gear. DPS is by far the easiest thing to get from mercs. Tanking is the worst, and healing is somewhere in the middle...if you have to choose between adding a healer box or a dps box I'd recommend healer box. I love my cleric, but I use him on raids quite a bit. Druids and Shamans also have their own personal flair if that is what you are looking for. ~MrGPAC
Go with the Shaman. Cleric merc augmented healing for tougher stuff as needed. Shaman can put out some pretty insane DPS while adding ADPS and buffs you cant get in the Merc world. Basicly your group will look like this ~ SK/Shm/Bard/WIz/Wiz/Cleric or Wizard as needed and you should be capable of killing 2million hitpoint trash mobs in the 30 second range with minimal difficulty and with Shaman healing and Merc cleric to help named mobs will be a push over. If like MrGPAC you already had a Cleric I'd might advise you to stay with it but starting fresh with one for use in the group game, I think even a Druid would make a better choice in higher end content since Shaman and Druid will both bring healing and something you can't get from a merc to your group.