• FactCheck.org - a nonpartisan organization that "aims to reduce the level of deception and confusion in U.S. politics." 

• PolitiFact -a nonpartisan fact-checking website that "rates the accuracy of claims by elected officials and others on its Truth-O-Meter." 

• Snopes - the oldest and largest fact-checking site online, Snopes reports on news, urban legends, & viral media, committed to "combating misinformation online"

Check out this analysis of the reliability of popular media. Sources used for factual research should be towards the top center of the media bias chart. 

NOTE: this chart - which is available to view online - rates popular media (news sources, blogs, and other websites). It does not include academic journals, which are typically found in subscription services.