Not too many, unfortunately. Of course, you wouldn't necessarily have to use fascism, you could use any recognizable totalitarian ideology. Perhaps Soviet imagery could have been used, or even more relevant in light of recent events, some of the Islamic theocracies or Arab dictatorships. Or maybe the point could have been made with text alone.
None of those possibilites would have illustrated the point as perfectly as the Nazi book burning picture. But they also wouldn't have produced the inevitable, immediate backlash that occured, and the subsequent retraction and bad publicity for WalMart.
LOL! Woooeee! Can you imagine the culture clash of an Islamoprotest at WalMart? Rednecks v. Rockthrowers! Gun nuts vs., well, nuts! I'd pay to see that!