Today, we discovered that a quotation we had always seen ascribed to Voltaire isn't actually something he said or wrote.
We refer, of course, to "I disapprove of what you say, but I will defend to the death your right to say it." ("Je désapprouve ce que vous dites, mais je défendrais à la mort votre droit à le dire.")
According to Wikipedia, Answers.com and several other sites we forgot to copy links to, that line appears in Friends of Voltaire (1907) by Beatrice Hall.
Something Voltaire did say, and which we saw for the first time today (yeah, we're borderline illiterate; sue us), and promptly fell in love with was: "Think for yourselves and let others enjoy the privilege to do so too." from Voltaire's Essay on Tolerance.