Clearly assuming the liberal standpoint on censorship, the ACLU presents a great amount of information, however biasedly, on the issue. Take what you read here with a grain of salt.
Supporting their often misconstrued theories, the Christian Coalition offers compelling arguments supporting censorship. Even if your values do not match those of the CC, it's a worthwhile website.
Site Index
Fairness and Accuracy in Reporting is a "media watch group" working to protect the First Amendment. It's often updated and contains lots of easily-accessible information.
A highly informational site dealing with fairness and unbiasedness in media. They're working to eliminate harmful stereotypes and abusive images from American television.
The American Family Association supports censorship and works to protect traditional family values. They want to help prevent America's moral decline.
Catholic Definition of Censorship
This Catholic Encyclopedia provides an interesting slant to censorship of books, from both historical and modern perspectives. It gives not only facts, but also the motives behind them.