I'm going to be bold and pick: Giants, Saints, Texans, and Broncos.
As said before, the Giants have a lot of momentum after steamrolling the Cowboys and pretty much shutting out the Falcons. Packers will certainly put up a fight, but that defense (next to dead last) could certainly be cause for concern against a fired up Eli Manning and company.
Saints don't play as well outside, but if Drew Brees can't go to the air, handing it off to Darren Sproles certainly seems like a good alternative. While San Francisco has a good defense, their offense has struggled in the red zone throughout the season. It's been said before: New Orleans is a team you can't beat with field goals. Provided they score, of course.
Texans over the Ravens because the latter has always struggled against the underdogs this season. Remember the losses to Jacksonville and San Diego earlier? Houston has shown that they can put together a competent offense with Yates, or maybe it's just because it was the Bengals, but I feel that Houston at least has a shot.
Broncos because they have momentum after Tim Tebow threw for 316 yards against one of the best passing defenses last week. New England's defense is dead last in ranks, so it's up to the Brady Bunch (Brady, Green-Ellis, Hernandez, Welker, and Gronkowski) to put up some points. Thing is, they've had slow first halves against Miami and Buffalo and fell down 2-3 scores. That could happen again, but they've always got it together in the second half. And remember: last year, the Patriots stomped the Jets 45-3 in their previous meeting but the Jets came and knocked them out in the first round. So I think Tebow Time still has some magic left.