"We are a nonpartisan, nonprofit “consumer advocate” for voters that aims to reduce the level of deception and confusion in U.S. politics." --from the web site of the Annenberg Public Policy Center of the University of Pennsylvania
A Pulitzer Prize-winning fact checking website that rates the accuracy of statements and arguments made by elected officials. Run by editors and reporters from the independent newspaper Tampa Bay Times, Politifact features the Truth-O-Meter that rates statements as “True,” “Mostly True,” “Half True,” “False,” and “Pants on Fire.”
The oldest and largest fact-checking site online, widely regarded by journalists, folklorists, and readers as an invaluable research companion.
Although The Washington Post Fact Checker checks more conservative claims than liberal ones, their checks are excellent and sourced, so you can follow up for yourself.
While not technically a fact checking site, AllSides pulls articles from the left, right, and center on political topics to give readers different points of view.
ProPublica is an independent, non-profit newsroom providing investigative journalism on political issues. Winner of multiple Pulitzer and other journalism prizes.