For a melee team, I'd go DK+2xPallies. You can have healer/tank/DPS trinity, and you can have a LOT of worthwhile melee buffs with those three characters (esp. if you spec DK as blood/frost).

For a ranged team, shaman are hard to beat. You get a team that can rez, heal, good totem defense.

You could also do druids and then have the option of doing any number of tank, healer, melee, ranged DPS setups.