You may have noticed that I occasionally refer to bane damage, which is not an official damage type. I actually got the idea from DDO, and feel it perfectly fits a rather specific place in D&D.
Anyway, here is a description of Bane Damage;
Bane damage is a kind of damage that cannot be reduced, resisted or negated by any means. It can be another form of damage, for example bane fire damage or bane cold damage, and it always ignores temporary hit points.