Four or Five Shaman, is a good group to start with.
The synergy is strong.
It's easier to box everything is the same.

If you want to do PvE stuff, consider going with either a Tank Druid (currently Feral; Guardian once MoP launches) or a Prot Paladin.

Tank: Druid or Paladin
Others: 4x Elemental Shaman



You can also mix it up a little.
More classes is a little more complicated.
But adds flexibility.

If your goal was/is PvE, dungeons too not just questing:
- Prot Paladin or Tank Druid
- 2x Elemental Shaman
- 1x Boomkin (if Paladin tank) or 1x Warlock (if Druid tank)... for the +Spell Power... and not overlapping buffs.
- 1x Healer of choice, Disc Priest or Holy Priest.