Zatanna's mythos isn't very deep. You basically have the "Zatanna's Quest" storyline from the 60s and Morrison's Seven Soldiers mini-series to draw from. She's basically been a supporting character otherwise, involved with John Constantine long ago, joined the JLA (with the most interesting thing being the "mind wiping" retcon), and had her father sacrifice his life to save his daughter in Alan Moore's American Gothic climax. There's stuff you can do with that, the Morrison mini-series in particular, but you're likely better off just taking the basic concept and going from there. Faust is an interesting suggestion for an opponent though.