Scion offered some good suggestions, item-wise, but there are a few more:
Standard of Heroism (Complete Warrior): +2 morale bonus to all saves for the wearer and companions within a certain radius. The +2 morale bonus to attacks and skill checks helps too.
Crystal Mask of MindArmor (X-Psi HB): +4 insight bonus to will saves for about 11kgp
Stone of Good Luck or 0-wishes Luckblade: about 20kgp for a +1 luck bonus to all saves.
So, with a +5 cloak of resistance, Crystal Mask of Mindarmor, Standard of Heroism, and the luckblade/stone of good luck, you would end up with +12 to your will save and +2 to many of your companions' for about 100kgp. Leaving the Standard and the Luck bonus out, you still have +9 for about 36kgp. Pretty cheap, all things considered. If you want more, the periapt of wisdom is less expensive than the luckstone or standard for the bonus it provides but it takes up a neck slot, only provides the bonus to will saves, and doesn't have the other benefits of the luckstone/luckblade or the standard. An Ioun stone of +2 wis is also a better deal per will save and doesn't take a slot but is limited to +2.
There are some other good mechanisms for boosting will saves:
Spells: At low levels, Remove Fear can be cast pre-emptively for a +4 bonus to saves. At mid levels, cloak of Bravery (Complete Warrior, cleric 3) provides a +1/clvl bonus to saves against fear to all allies and Heroism provides a +2 morale bonus to all saves (and attacks and skill checks) to one target, at high levels, Greater Heroism (Sor/Wiz 6), and Hero's Feast provide immunity to fear. Hero's Feast provides a +1 morale bonus to all will saves as well. At very high levels, mind blank offers almost complete immunity.
Prestige Classes: Occult Slayer (Complete Warrior) offers considerable protection against mind-effecting magic. Three levels of Holy Liberator (Complete Warrior) also offers good protection. The Pious Templar (Complete Divine) has good will saves as well though it doesn't offer immunity to wide classes of spells like the Holy Liberator or Occult Slayer.