I think the Broncos can beat them. The Broncos are like the Pats in the way their team is improving as the year goes on. They actually have some pass rushers on the team, and they can score. Home field would be huge in that game. Don't discount the effect the thin air would have on the Pats going hurry up all game long.
Maybe the 49ers. They are so up and down. At their best, their D is just physically crushing people. At their best, I would not be surprised (not wishing for it) to see Welker carted off after going over the middle.
Giants, when playing well obviously can. The thought of another Giants/Pats Super Bowl makes me want to follow Hockey instead of football. At least in Hockey, your team never loses (of course your team never plays either)