if you wore to do sacred vow with an evil deity or for an evil cause, I don't see an issue making that exception if your DM is cool with it.
But Vow of nonviolence might have conflicts through the game.
Theres lots of stuff in the magic item compendium
But this is what really cough my eye.
ANKH OF ASCENSION
Price (Item Level): 9,000 gp (12th)
Body Slot: Throat
Caster Level: 17th
Aura: Strong; (DC 23) conjuration
Activation: Free (command)
Weight: 3 lb.
Crudely carved from splintering wood and dangling from frayed twine, this simple ankh looks brittle and ancient. When you activate an ankh of ascension, you must sacrifice a prepared divine spell or divine spell slot. The caster level of any divine spells of that level or lower that you cast before your next turn increases by 4. An ankh of ascension functions three times per day.
Prerequisites: Craft Wondrous Item, gate. Cost to Create: 4,500 gp, 360 XP, 9 days.
