These can be useful sites in pursuing critical analysis of news, but keep in mind that they themselves may not be free of bias, poor context, or misrepresentation.
Check out the discourse in the following articles from 2011 to see the issue in a little more detail:
Lies, Damned Lies, and 'Fact Checking': The liberal media’s latest attempt to control the discourse
Here's a more recent analysis of fact-checkers:
The 2016 guide to political fact-checking on the internet
"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. . . .PolitiFact staffers research statements and rate their accuracy on the Truth-O-Meter, from True to False. . . .PolitiFact checks claims by elected officials, candidates, leaders of political parties and political activists. We examine officials at all levels of government, from county commissioners to U.S. senators, from city council members to the president."
"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. Our goal is to apply the best practices of both journalism and scholarship, and to increase public knowledge and understanding. FactCheck.org is a project of the Annenberg Public Policy Center of the University of Pennsylvania."
What began in 1995 as an interest in documenting and uncovering urban myths is now considered one of the most essential tools of the Internet. Snopes is an independent site funded by advertising revenue, and it covers an astonishingly large number of topics with source citations in each article.
Below are tools that can be installed in your browser to alert you to potentially fake news. Keep in mind that fake news involves many factors, that plug-ins (like fact-chacing sites) rely on potentially biased input, and that no internet application is able to perform critical analysis the way your brain can. Although these may be useful starting places, use critically and with caution.