Now that we have taken the necessary first step to regard the English Wikipedia and other Wikimedia projects as high-profile platforms for political statements, we ought to consider what other critical humanitarian problems we could use our considerable visibility and reputation to address. We could draw attention to the crises in Sudan or Nigeria, drone attacks against civilians in Afghanistan, the permanent occupation of the Palestinian territories, the Iranian effort to develop nuclear capabilities, police misconduct in virtually any country, the treatment of women and women's rights in Saudi Arabia and elsewhere, and the list could go on and on.
There are so many good candidates, in fact, we will need some way of narrowing them down. A SOPA protest fits a somewhat narrow range - a United States law that could effect a Wikimedia project. We could protest against the Patriot Act, warrantless wiretapping laws, national security letters, unpublicized cooperation between major ISPs and national intelligence agencies, laws that allow speech online to be deemed "material support and comfort" of a terrorist group, etc. etc.
Of course, there is no articulated reason to limit ourselves this way. Surely a large portion of our voting community would be against pending attempts to restrict free speech on the Internet in India (a nation with many English speakers and many Wikimedians, and an office of the WMF). I can't imagine we would get much opposition to a protest against censorship and filtering in China, which has more Internet users than any other nation and represents a vast untapped resource for the open source and open knowledge community. Many other countries filter or block our content to the detriment of their citizens, and we could surely add pressure and attention to these important issues.
The possibilities are, quite unfortunately, nearly endless. Obviously we can't keep Wikipedia offline and just rotate the protest message; perhaps we should consider creating a Campaign of the Week (or Month?) to highlight humanitarian problems. All we need are volunteers to set up a Wikipedia:CotW and get it rolling, and we can start to make a real difference.
Nathan