The cleric in one of the games I play in uses a Spell called "Essay Resistance" or something like that. I don't know which book its in, but it is great for reducing a targets SR. It gives the target a major penalty on the save to resist the spell, but if the spell works the targets SR is reduced by 10 or more points, which helps even the Arcane Spell Caster to be more effective.
Consider a weapon ability called Sure Striking, its great for overcoming DR. Basically it will overcome DR based on alignment. So if your +2 Sure Striking Heavy Mace hits the big bad guy with DR 15/ alignment, it should go through.