EricNoah said:2) The remaining creatures should either simply be magic immune (a rare minority in my opinion), or should be noticibly harder to effect with magic. To accomplish this, give a small bonus to saves vs. magical effects (+2 to +4), and maybe grant them a kind of "magic evasion" -- full effect on a failed save, no effect on a successful save. [I personally don't even think this last bit is necessary, but it at least mimics the standard SR rules a bit more closely.]
You know, someone else posted about getting rid of SR, and I was thinking of the exact same thing as you just suggested. It could be a monster feat or quality or something......
So SR could be as simple as the creature having a racial bonus to saves vs. spells, and then this feat, so that if they make their save, they evade the spell.
The only downside to that is it removes any kind of influence by the spellcaster's power, which was a fix in 3E to the idea in 1st and 2nd Ed. that magic resistance was all or nothing.
Banshee