I'm vaguely remembering someone in a novel raging in battle and not remembering anything until the battle was won, but drawing a blank. I know it wasn't in "Three Hearts and Three Lions" despite there being a similar scene in that, because Paladin, not barbarian. If I can remember it, I'll come back and post it too.
I think that my favourite is not actually borne of anger, but fear. An "urban barbarian." In "The Horseclans" series of books Geros Lahvoheetos is a gentleman's servant who, during an ambush, is sent off for help. He has no weapons training and considers himself to be a coward. They give him a mule and a spear. No armour. No one else to go with him, because no one else can be spared. Off he goes for help. A short distance along the road he comes upon three raiders who raise their weapons and move to attack, Out of terror he spurs him mule forward. Not being trained he swings his spear like a staff, forgetting that it has a bladed point, and cuts the throat of one of one, then rides right over another of the raiders, while accidentally jamming his spear into the third. He has no clear memory of this, since he's terrified and pretty much has his eyes closed through the whole incident.
When he returns with reinforcements his master, who thought that he was just going to be dying a little before the rest of them did, thinks that he has underestimated the "natural talents" of Geros. He's armed, equipped, and added to the common soldiery. Realizing that he needs to get a quick education or die quickly, he starts mastering his weapons. It doesn't help with the fear. In his first real battle his internal monologue is damning his luck, damning the enemy for making him fight, and damning himself for his own cowardice. This goes from an internal monologue to externally shouting, "DAMN YOU! DAMN YOU!", which his fellows take to be his battle cry. Again, everything is pretty much just a blur of hoof beats, flashing metal, and blood; no real memory.
Along the way he's congratulated for his valour by his legendary captain (Billy the Axe). Geros can't accept the praise stating, with great embarrassment, that when the battle came, he pissed himself. All of the leaders present laugh at this and Geros is concerned that his cowardice is now in the open, for all to see. Billy reassures him that they weren't laughing at him, but rather because it's such a common thing. In fact [insert famous general's name here] would routinely crap himself when going into battle. Billy says that any man who isn't afraid when going into battle is a fool and not someone he'd want at his side.
So fear, not anger sparking a barbarian "rage."
