Faiths & Pantheons has the prestige Auspician, which gives you Fickle Finger of Fate, which is like Luck domain except that it makes another reroll -- enemy or ally (I believe Fatespinner still gives this too). It's 3.0 technically, but afaik requires no updating for 3.5 games.
For something exotic, now: Polymorph Any Object your familiar into a Vasuthant (MMIII). Its Reality Distortion ability forces three rerolls per day. Normally an offensive ability, but very nice for making saves as well.
It's a free action to activate, so the familiar needs to ready an action to do it.
There's the Devil's Own Luck feat from WoT, but that's not D&D. I don't see a problem with allowing it, though (IMO, WoT is really underpowered compared to D&D anyway).