Figured this was as good a thread as any to post some links to fact-checking services as well. Please bear in mind, that just because 'fact' may be in the name, doesn't make so. Don't be surprised if your argument is still held under scrutiny or challenged in a debate. It is up to you to defend your statements.. these sites are only to aid you in your search for sources.
FactCheck.Org - Most recognized political fact-checking site I can think of.
PolitiFact - Another political fact-checking site by St. Petersburg Times
Truth Or Fiction - Fact-Checking/Rumor-Checking site on a number of different subjects. Politics, Religion... etc. Seems to be news/headline related concerning the section topics.
If you have more links to fact checking, rumor checking or any other (non-partisan, non-profit) source related sites... please feel free to share the links.