Here are some specific suggested resources:
PolitiFact - From the Tampa Bay Times, this fact-checking website won a Pulitzer Prize in 2009.
Snopes.com - Billing itself as "the definitive Internet reference source for ... misinformation", Snopes.com double-checks a wide range of claims, from urban legends to Internet rumors.
What Comes Next? A Resource Guide zine (and call to action) from Hunter College Libraries. How to think critically about your information sources