Ok, I did a quick run through ThatWhichShallNotBeNamed*, and it seems Charisma is the save against planar binding or banishment (Divine Word, Forcecage, etc) as well as spells that effect emotion (Calm Emotion, Symbol) and Truth (Zone of Truth). Cha is used for spells where you test your presence against another, rather than those that test your willpower.
Intelligence seems very much the area of psionics; spells that affect your mind (Feeblemind, Symbol of Madness) or use your brain to kill you (Phantasmal Killer, Weird) seem to be the Int save areas. I'm sure Mind Blast and the eventual Psionicist are going to have a field day with this.
Strength saves are against physical restraint or movement: Entangle, Gust of Wind, Thunderous Smite's knockback, the winds of a Tsumani or Wind Wall spells, etc.