What class would round out this group best?

[mr_jon3s]

Enchanter hands down. Gives 4 people clarity and charm pets just do so much DPS.

[thufir]

Enchanter or shaman. Enchanter is better (and provides the extra dps your group is missing), but shaman is fine. Bard slows are acceptable right now but the higher level you get the less acceptable they will be. (The bard should still pre-slow.)

[Halfelfbard]

Rogue, and it depends on how good ur bard is...otherwise enchanter. If you snare kite with the bard you can dps the hell out of the mobs with a rogue.

It really all depends on the player it doesn't matter what class it is.