How can I reduce/ignore any damage reduction with weapon attacks?

I know the Mountain Hammer line from Tome of Battle:

> 
> As part of this maneuver, you make a single melee attack. This attack deals an extra 2d6 points of damage and automatically overcomes damage reduction and hardness.
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> 
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I am looking for a way to get this effect of overcoming damage reduction on a full-attack.

I *think* I have seen a "reduce any DR by 5" feat, but I can't remember where.

Permanent solutions are preferable, and official books.