Take a vow of poverty, silence, or mercy.
I'm particularly keen on the vow of mercy - the other players don't really like the whole 'I'm not going to kill anything that isn't stinking with evil AND an immediate threat to our safety... I might fight it to unconsciousness, but the give it a chance to redeem itself... not going to kill it outright' thing, though.
Doesn't mean that you *can't* kill... but, that you will not kill so much.
I really like the idea of giving up the ability to rage... it sucks, true. But, eventually maybe it could be replaced with a Religious Zeal for your particular God? ... could easily be worked into a vow of mercy.