OK, I'm not sure I buy Zatanna as a hat wearing super chick mostly because of all the years I read her adventures with the JLA where she had that strange lobster hair clip.
Essentially she's hear now because of her huge resurrgence as the hard luck sorceress of late from DC's Indentity Crisis and Seven Soldiers series.
She also has the benefit of having a power that is both visually interesting and annoying as hell at the same time. She speaks her spells backwards. I'm also willing to say that she's generally sort of distracting in a...Power Girl sort of way. Between her and Black Canary, there wasn't a pair of fishnets in the DCU that wasn't already accounted for. They must have cost $40 a pair.
She comes from a magical family as well. Zatara, her father taught her the whole backwards speak schtick and she has a cousin, Zachary Zatara who is a snot nosed punk who once joined the Titans off screen and then annoyed the piss out of them.