Combating Online Infringement and Counterfeits Act (COICA)creates two blacklists of Internet domain names. Courts could add sites to the first list; the Attorney General would have control over the second. Internet service providers and others (everyone from Comcast to PayPal to Google AdSense) would be required to block any domains on the first list. They would also receive immunity (and presumably the good favor of the government) if they block domains on the second list.
The lists are for sites "dedicated to infringing activity," but that's defined very broadly -- any domain name where counterfeit goods or copyrighted material are "central to the activity of the Internet site" could be blocked.
S. 3804: Combating Online Infringement and Counterfeits Act Link: http://www.govtrack.us/congress/bill.xpd?bill=s111-3804