In the 3.0 book "Masters of the Wild" page 18.
[spoiler]
Variant Intimidation Rules
It's an unfortunate fact that the barbarian, regardless of his might, can still fail to intimidate foes who are cowed by the stylish bard or the magnetic sorcerer. The two optional rules presented here are designed to make the barbarian a bit more frightening. These rules work whether the barbarian is raginr or not, though rage does increase their effectiveness.
Raging Intimidation
Barbarians get a +4 intimidation bonus while raging
Intimidation through Strength
Use Strength instead of Charisma when making intimidating checks. This assumes, of course, that he accompanies such attempts with appropriate displays of might, such as breaking objects or showing off impressive muscles.
[/spoiler]
