A coalition including the EFF, Mozilla, Creative Commons, Wikimedia, and many other organizations have been rallying internet users to contact Congress and expression their opposition to SOPA. Over a million emails and thousands of personal calls were sent to Congressional representatives.
With the I Work For the Internet petition, you can join thousands more in showing your support to stop this bill. Here’s an I Work For the Internets t-shirt that found it’s way there. ^^
For more info on SOPA and its threat, read up on the EFF’s excellent coverage.