Time Magazine captured an anti-Gingrich ad that was accidentally posted on a Romney Super PAC page and then immediately taken down. It's not a direct attack on Gingrich from Romney, but it is by far the most negative Romney's people have gotten:

Important to note: This ad isn't as harsh in its anti-Gingrich rhetoric as some of the Ron Paul ads that have popped up in the last few days. Maybe the Romney Super PAC just needs to fund those Paul ads in Iowa instead of this ad, which promotes the fact that Gingrich approved a health care mandate, which in turn opens Romney up to a whole new tack of health care questions.