Sites like Wikipedia and Reddit have gone black today to protest anti-internet piracy bills Stop Online Piracy Act (SOPA) and Protect IP Act (PIPA). Concocted by Texas Republican Rep. Lamar Smith, SOPA would "require websites to delete links from their search results to websites deemed 'illegal,' and that all the anticipated SOPA and PIPA-related lawsuits would make the cost of creating an internet startup too high." Contact your senator or make a call to your representative.
As SFist commenter tarniv points out, this is not just a Republican travesty. Sen. Barbara Boxer and Sen. Dianne Feinstein not only support of PIPA, but co-sponsored it as well. You can call them to leave them a polite message at 202-224-3841 (Feinstein) and 202-224-3553 (Boxer).