Recently, we've been chatting quite a bit about the Entertainment Software Association, and its involvement with SOPA. The ESA is a trade association, looking after the interests of videogames while pretending to fight for free speech and gamer causes. The ESA's support of SOPA pretty much confirms that its Videogame Voters Network is little more than insincere astroturfing, but the ECA is on the level.
The Entertainment Consumers Association, unlike the VGVN, is an actual gamer advocacy group, and has been fighting against SOPA as well (it's also been incredibly supportive of Destructoid's efforts). If you care about the rights of videogame consumers, it's pretty much the best place to start.
Like Destructoid, the ECA has provided gamers with some help in getting their voices out about SOPA. This page contains information on the bill and useful tools in getting your message out to the people that matter.
They do good work, so check them out!