IMC, right now there's a demon that's following the party around, tormenting them. Its powers include invisibility, flight, major image, hold person, and suggestion, all at will.
It's having a great time with the two fighter-types in the party: their low will saves mean that he's gotten several occasions to use hold person and suggestion on them. He keeps hoping to successfully hold a fighter and then CDG him, but luck and tactics on the party's part have prevented that so far.
Here's how my party has handled the low saves of their brawny guys:
-Protection from Evil: Super-important, as it protects against compulsion effects such as suggestion and (I think) hold person. They keep a magic circle against evil and a couple of protections against evil prepared at all times.
-Lion's Heart: there's a spell in Relics and Rituals that gives a character 5 points to spend on fortitude and/or will saves. It's a high-level spell, but the party cleric makes sure that everyone has this spell on them at all times. When the demon uses his mind-control tricks, people generally blow all five of their points to resist him.
-Protection Domain: The domain power helps with saves, and the party cleric uses this when they think they might encounter the demon.
-Dispel Magic: two different party members keep this spell prepared, ready to use it if a really nasty effect occurs.
-Cloaks of Resistance: These have gone to the fighter-types, since their weakness versus will saves seem to be exploited most often (as a DM, I love enchantments and illusion magics).
I agree that this is a weakness that fighters have. However, if fighters have spellcasters in the party, they can get some help with it. It's actually much more of a problem for critters like giants, who don't generally have spellcasters handy to help them out. And last session, the badass shadowdancer that attacked the party with his thuggish minions was laid low by a single hold-person spell; too bad for him that he didn't have a badass cleric helping him out!
Daniel