A nice place to have a look at for a Bard is:
http://www.theconcerthall.net/phpBB3/index.phpHere some random thoughts:
For 2-box:
Sk + DPSmerc + healermerc. Will allow you get the furthest. Maybe once ready for UF you would swap in a second healermerc.
Bard+SK + mercs should allow you to do all SOD and afterwards you should be able to farm some UF-mobs as well.
After SOD Tankmercs are done. You either need a real Tank or a Magepet if you want to do UF-content.
Bard himself can tank to an extend but has it really hard to keep aggro against dps-classes.
If you are thinking about shaman + dps-merc, it will be hard to stay ontop of aggrolist.
Shaman + tankmerc will do til SOD done, but I think not anymore in UF.
Paladin is a nice tank, but by himself doesn't offer as much dps as a SK can offer.
For full groups the additional heals and cures may be even better for some bad nameds to bring them down, there are sufficient other chars to deal the damage.
For a low-members 2-box it's more important to have sufficient dps on your chars than for a full group, so for this setup I would prefer the SK.
To get a mob down you can do so with 2 different approaches:
One is the attempt to have enought healing and cures to endure for a sufficient time everything a mobs can throw at you and let the dps bring him down.
The other one is just dealing sufficient amount of dps, so that the mobs hp-bar goes down faster than your tanks hp-bar.
My core group of eq-friends since ages contains a paladin and a cleric. So 2 priests + a paladin are able to endure a lot of stuff a mob may offer.
When I am out on my own for boxing, I do it the other way, I rely on merc-healers and kill the mobs befor they get me.