Dwarf Elemental Shaman?
Seriously, though, play what you want, not what you think the guild needs. You have an Elf Mage and a Human Warlock. My suggestion would be to make a character that fills a different role (tank, heals, melee dps) and/or try a different race so you can experience a new starting area (worgen, dranei, gnome, dwarf).
Here is my rundown of the classes and their roles:
Paladin: tank/melee dps/heals
Druid: tank/melee dps/ranged dps/heals
Warrior: tank/melee dps
Death Knight: tank/melee dps (and start at level 55)
Hunter: ranged dps
Rogue: melee dps
Shaman: heals/ranged dps/melee dps
Priest: heals/ranged dps