It would seem that everyone has said it. But, again, yes, Fighters Are the feat man. They get 18 in comparison with everyone else's 7. Yet another if they're human.
There's the Iron Will, or Arcane Defense (Tome and Blood) that gives a +2 vs. a magic school's DCs. If you're Really up a creak, why not play a Dwarven fighter, who gets an extra +2 to saves vs. magical stuff? Elves are immune to sleep and recieve a +2 vs. Enchantment spells, where a lot of your Will spells come from. If you're Really afraid, ask the cleric or wizard to slap a Protection from Evil spell on you. It's cheap, and effective vs. some mind effecting spells. If you're die hard about resisting them, then play a Native Outsider (Genasi, Tiefling, etc); they're immune to Charm, Hold Person, Etc.
Hey, there are quite a few spells that effect Fort saves. Disintegrate, Blindness/Deafness, Polymorph Other... Mages are just as weak. And, Phantasmal Killer has TWO saves, so it should help you out somewhere.
Really, my party's ground is well covered. An Illusionist, a cleric, an NPC true lycanthrope, and a half-dragon thief. Their saves all around are good, and the Lycanthrope's not effected by Person spells.