If you care about free speech, please read this
As the Electronic Frontier Foundation puts it: "PIPA and SOPA . . . would drastically change the way we use the Internet (for the worse), and punish millions of innocent users who have never even thought about copyright infringement. . . . These bills must be stopped if we want to protect free speech and innovation on the web."
If you're a U.S. citizen, you can contact Congress through this online form or through this EFF site. In addition, Dreamwidth Studios suggests, "If you are not a United States citizen, you can still help. Spread the word about these laws. If passed, this will not just affect people who live in the US - it will affect everybody who uses web sites based in and/or owned by American businesses."
Wherever you live, please pass on the word, in the same manner that you would pass on the word if you heard that your favorite writer had been censored. These bills threaten the free speech of everyone.