As the examples mount up, it's impossible to point to any lie which stands above the rest; but the Romney video of Obama's words about business-builders is about as exemplary as it gets. He'll try, but he'll never top his way (the copyrighted RWS™/Republican politician way) of accusing his opponent of doing that which he's done himself. Because, in this case, he actually had to decontextualize and edit what his opponent said, and then hide the fact that he's said it himself. (And, amusingly enough, that the featured businessman in his dishonest ad got $800K of government help, righteous claims to the contrary notwithstanding.)
So Barack Obama made a statement about how success in America never happens alone: you had teachers, you drove on roads someone else built, you probably used a light bulb at some time and likely used indoor plumbing... you know, something so obvious it's been said before by such people as Elizabeth Warren and FDR, and that flaming liberal (well, he was once, by comparison) Mitt Romney.
Take something Obama said, make it sound like he said the opposite, then say what he actually said yourself. Gotta hand it to the guy: I mean, that's third-order dishonesty, raising the bar to impossible levels. Obama's statement is true. Everything Romney says about it -- as is the case with everything else he says about Obama -- is false.
Wingers, of course, see the ad as a "game changer", and who can say they're wrong? Because it's obvious that the fewer the facts and the more the mendacity the better they buy it. But it hardly changes the game. Not their game, anyway. It's exactly the way they've played it since Newt and Karl came on the scene; and, as sure as dogs get diarrhea on car roofs, it'll persist until conservatives demand better.
Forever, in other words.