Some multiclassing ideas
Unusual Barbarian Roles:
The Shaman, educator of Chieftans, healer of the people- Barbarian/Druid, Barbarian/Cleric or Barbarian/Sorcerer
The Diplomat speaking eloquently about just how his Chieftan will be using the skulls of invaders as soup bowls- Barbarian/Druid, Barbarian/Cleric, Barbarian/Bard
The Promised One who will lead his people to greater glory- Barbarian/Druid, Barbarian/Sorcerer, Barbarian/Ranger, Barbarian/Fighter, Barbarian/Soulknife or Barbarian/Psionic Warrior
The Skald who sings the songs of heroism to inspire his allies or impress his foes- Barbarian/Bard
The Keeper of Tribal Histories, including past slights and insults, and tribal boundaries, he decides when to advise a Chief to go to war...- Barbarian/Bard, Barbarian/Cleric, Barbarian/Druid, Barbarian/Ranger
The Hidden Hand of Kord, an infiltrator who gathers intelligence or smites enemies at any time, anywhere- Barbarian/Ranger, Barbarian/Rogue, Barbarian/Bard, Barbarian/Soulknife or Barbarian/Psionic Warrior.
Remember- Bards can cast spells in light armor...meaning as time goes by, he could use something as good as a Mithril Breastplate for armor while still casting without ASF, and Divine spellcasting and Psionic Abilities are completely unaffected by armor.
Clerical Domains that work well with barbarians: Any elemental, Travel, Strength, Animal, Plant, Destruction, Death, Good, Healing, Chaos.
Weapons I like for barbarians- Lt or Hvy Flail, Greatspear, Maul, Warmace, Greataxe, Dwarven Waraxe, Longbow, Morningstar, Greatsword, Spiked Shield, Spiked Gauntlet.
Feats I like for barbarians: The Power Attack Feat Tree, Monkey Grip, 2wf, Improved Shield bash, IUC, the Expertise Feat tree, XWP (Maul, Dwarven Waraxe, Warmace, or Greatspear), Combat Reflexes, Oversized 2wf, Extend Rage, Extra Rage, and whatever that one that lets you cast spells while raging are all cool with me.