You need to do two things. A: Maximize your to-hit. Once you hit things, you're half way home. I suggest something like Compression to reduce your size to tiny or smaller for a gigantic to-hit and AC bonus. You'll lose some strength, so you might need to go for weapon finesse with a spiked chain. The signature ability of the barbarian is the ability to hit things and deal a fuckton of damage, which leads me to my next point:
B: Maximize your power attack and charge damage modifiers. Frenzied berserker, leap attack, shock trooper, valorous weapon, battle jump, it's all good. You can get a humongous modifier on your damage, even if your weapon only deals one damage, you'll add on 100 for leap attack shock trooper, x2 for a valorous weapon, and whatever the hell battle jump does, resulting in 200+ damage per hit.
Yeah, okay, but what can you do that a regular barbarian can't? Nothing, really. You will desperately need a way to consistenly charge your opponent, and a way to avoid provoking his AoOs. So get yourself an item of continual flicker and an item of continual invisibility. This way you'll have total concealment vs your opponent, allowing you to enter his square freely, and you'll be able to teleport 10 feet back as an immediate action every round, thus, if you take whirling frenzy, you're looking at a damage output of 400-1000 per round, going from 2 hits to 5 hits. You'll need to make sure that you never lower your strength below 13, or you lose the benefit of the power attack feat, but between whirling frenzy and a modest strength boosting item, you won't really care. Plus, you'll have the highest AC of a barbarian in recorded history.
Finally, it is of note that Favored Power Attack could be worth it, assuming you're just out to hunt one type of thing. Also, take Confound the Big Folk ASAP.
