Discerning the truth about political facts and claims is an onerous and unfulfilling one. What you're most likely to find is that, by and large, everyone lies or distorts. Certainly, no televised advertising can be trusted (this seems given), the candidates are going to present their case in the most favorable light possible, and we cannot rely on journalists to present any kind of useful analysis, a small handful aside.
The two best sources I've found so far, FactCheck and Politifact are certainly useful tools, although they require a good deal of time to wade through to understand the often shaded nuances (outright fabrications are easier to sort out) of the claims made by politicians, PACs, SuperPACs, and other partisan organizations. Sometimes, the About page on Urban Legends and Netlore is useful, and Snopes can be good where more personal claims are made (e.g., Q: Is Hillary Clinton the liberal Marxist America-hater I know she is? A: If you take her statements out of context, she's handing America over to Fidel Castro right now.) None of these sources are infallible and both liberals and conservatives alike have taken specific aim at Politifact from time to time, but these sites do try to lay out data as much as possible
I wonder how widely these (or other reliable) sources are used and who uses them? I'm inclined to think only those most invested or interested in political discourse and strategies do--with most people leaning on soundbites offered on broadcast news, entertainers (e.g., Limbaugh, Beck, Palin, Stewart) primarily, faux-political commentors (e.g., Hannity, Van Susteren, Schultz) and, to a lesser extent, partisan wonks (e.g., Huckabee, Maddow). Confirmation bias (i.e., the theory that we seek and ignore evidence in ways that help maintain the beliefs we want to maintain) is a real threat for people of all political inclinations. And, existing research suggests that getting people to re-think their deeply held beliefs, even opposing factual evidence is offered, is very difficult anyway.
As an example, I'll use the above popular macro, seen circulating on a Facebook page near you, to illustrate how difficult discerning such claims can be, or at least how much more complex such claims are.