Currently playing with a DK-tank, Disc, Shaman, Hunter and a mage and it works very well.
I tried every tank and decided that the dk is far the best for a pve-team.
No healer needed in a hero until expansion

For WoD Im leveling a new team to fit the new buffs. Disc will get a nerf and ele lost their healing tide totem.
So i will switsch my healer to a druid and my shaman with a shadow.
But I will miss the extra dmg from the healer