The Rules of Civil Conversation is a website designed to help visitors better understand how to hold a civil conversation in the face of differing opinions. One of the resources on the site is a set of posters outlining eight rules of civil conversation. These posters can be downloaded for free and printed for display in your classroom. (There is also an option to buy printed versions).
School of Thought also created the sites Your Logical Fallacy Is and Your Bias Is. I've previously featured those sites in my larger collection of resources to help students recognize logical fallacies and cognitive biases.