Dan GillmorIran's Net Censorship
Hoder points me to "Stop Censoring Us" -- a site about the increasing level of government intervention in what was emerging as relatively free speech in Iran. I'm not sure what individuals outside Iran can do about this except to offer support to the Iranians who want to speak their minds.
I once sat next to a guy from Sun Federal, a Sun Microsystems subsidiary, who was on his way back from selling a filtering system to a government. I think that most of this censorship technology is built in the US. I guess it makes sense, but it's interesting that there is very little discussion about this. (At least as far as I know...)