Pennsylvania Gov. Ed Rendell (D) vetoed legislation Monday that would've required voters to present valid photo ID before casting a ballot. His veto notwithstanding, many states have enacted similar legislation in the last year.
Perhaps the controversy is most heated in Georgia, where a federal court threw out a law passed last year. There, lawmakers passed another version of the law in January. For some good background on the issue, check out the Stateline.org story from last spring, when this movement started picking up steam.