Snopes claims to be "the definitive Internet reference source for urban legends, folklore, myths, rumors, and misinformation."

PolitiFact is a fact-checking website that rates the accuracy of claims by elected officials and others who speak up in American politics. PolitiFact is run by editors and reporters from The Tampa Bay Times, an independent newspaper in Florida... (from their web site)

We are a nonpartisan, nonprofit “consumer advocate” for voters that aims to reduce the level of deception and confusion in U.S. politics. We monitor the factual accuracy of what is said by major U.S. political players in the form of TV ads, debates, speeches, interviews and news releases. FactCheck.org is a project of the Annenberg Public Policy Center of the University of Pennsylvania. (from their web site)

AllSides provides multiple perspectives on a single issue.

PunditFact is a project of The Tampa Bay Times and the Poynter Institute, dedicated to checking the accuracy of claims by pundits, columnists, bloggers, political analysts, the hosts and guests of talk shows, and other members of the media. (from their web site)

Nodes of Science is a collaborative science communication and outreach network promoting skeptical inquiry and scientific reasoning throughout social media. (from their web site)