Basically, the subject line says it all. I've looked over the harm spell, it's way too overpowered for my game, and I've heard talk of a harm houserule, wanted to know what it was or, barring that, where to find it.
I think the general consensus on Harm is that it's fine if you allow a Fort save to negate. Another alternative is if you make a Fort save, you only loose half of your current remaining HP's and drop to 1d4 if you fail.