FactCheck.org (Annenberg's excellent nonpartisan political fact checker--monitors 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.
See also Hoaxes, urban legends, and email scams
PolitiFact.com (nonpartisan political fact checker, whose truth-o-meter ranks findings from "true" to "pants on fire"). a project operated by the Tampa Bay Times, in which reporters and editors from the Times and affiliated media outlets "fact-check statements by members of Congress, the White House, lobbyists and interest groups."
The Fact Checker (Glenn Kessler's Washington Post column, The Truth Behind the Rhetoric, fact checks statements by politicians and political advocacy groups and doles out Pinocchios on politician's statements that don't pass muster)
Regret the Error (Craig Silverman, on Poynter site, reports on trends and issues regarding media accuracy and the discipline of verification. Stories about errors, corrections, fact checking and verification.
Accuracy in Media (a conservative citizens' watchdog group for fairness, balance and accuracy in news reporting)
Newsbusters ("exposing and combating liberal media bias")
Fairness & Accuracy In Reporting (FAIR) (Challenging media bias and censorship since 1986), a national progressive media watchdog group, challenging corporate media bias, spin and misinformation.
Media Matters for America (MMfA), a politically progressive media watchdog and advocacy group with a stated mission of "comprehensively monitoring, analyzing, and correcting conservative misinformation in the U.S. media."
OpenSecrets.org (Center for Responsive Politics--advocates for transparency in government, monitoring campaign contributions and lobbying, to measure their possible effect on U.S. elections and public policy)
The Cochrane Collaborative (systematically reviews and evaluates research in health care and health policy)
Quackwatch (your guide to quackery, health fraud, and intelligent decisions, operated by Stephen Barrett, MD)
The Straight Dope (Cecil Adams) Check message boards.
Bad Science (Ben Goldacre's column from The Guardian in weblog format. Covers media misrepresentations of science, especially medicine, by the author of Bad Pharma: How Drug Companies Mislead Doctors and Harm Patients
The Skeptic's Dictionary (exploring strange beliefs, amusing deceptions, and dangerous delusions since 1994)
FourMatch (Authenticate images instantly. An extension for Adobe Photoshop that instantly analyzes any open JPEG image to determine whether it is an untouched original from a digital camera. Now, you can quickly identify files that have not previously been edited.)
On the Issues (every political leader on every issue)
Tin Eye (Idée's a reverse image search engine). You can submit an image to TinEye to find out where it came from, how it is being used, if modified versions of the image exist, or to find higher resolution versions.
Miscellaneous research tools (SPJ, Journalists' Toolbox)
New York Times Newsroom Navigator (Rich Meislin)
NY Times Business Navigator
NY Times Politics Navigator
NY Times Health Navigator
E-mail story sound too good or scary to be true? Check to see if it's an urban legend. Several websites are devoted to fact-checking and identifying hoaxes and urban legends. Before you forward that "true fact," e-mail petition, warning, amazing opportunity, or piece of gossip, run it by one of these sites.
Snopes.com, on which Barbara and David Mikkelson try to debunk and validate urban legends, folklore, myths, Internet rumors, misinformation, and other stories of uncertain origin. An independent entity owned and operated by the Mekkelsons, who say they receive no funding in any form.
Truth or Fiction (another reality check on email hoaxes, rumors, scams, and advisories--to verify the truth or falsity of rumors, inspirational stories, virus warnings, humorous tales, pleas for help, urban legends, prayer requests, calls to action, and other forwarded emails)
Verification Junkie (Josh Steams' directory of tools for verifying, fact checking and assessing the validity of social media and user generated content)
Is Twitter Wrong? ( public service pedantry hub. run by @flashboy, who sometimes retweets stuff without fact-checking)
Quatloos (check out financial scams and fraud)
Sree's tips on hoaxes
Current hoaxes and legends (About.com)
Hoax Busters (verify virus hoaxes, chain e-mails and urban myths)
How to Determine If A Controversial Statement Is Scientifically True (Alan Henry, Lifehacker, 6-20-12)
The Red Tape Chronicles (Bob Sullivan, MSNBC, looks at Internet scams and consumer fraud)
Consumerist (a consumer affairs blog, hosted by a division of Consumer Reports)
Urban legends, fact-checking (Journalist's Toolbox, SPJ, excellent links)
VMyths (Truth About Computer Security Hysteria)
Symantec Threat Explorer (a comprehensive resource for daily, accurate and up-to-date information on the latest digital threats, risks and vulnerabilities)