Arakhor, these are how I've modified Iron Will and Lightning Reflexes. Both are reasonably popular (About as popular as my Great Fortitude, and way more popular than any of the save boosting feats were in my group before).
Lightning Reflexes (Fighter)
You have faster than normal reflexes.
Benefit: You get a +2 bonus on all Reflex saving throws and may make one additional attack of opportunity each round.
Iron Will (Fighter)
You have a stronger will than normal.
Benefit: You get a +2 bonus on all Will saving throws and may reroll a single failed Will saving throw each day.
Cheers.