Andy Roddick. I never thought I'd be saying the biggest cinch to make the semis isn't named Nadal, Federer, or Djokovic, but I don't even think it's debatable. He drew Davydenko's quarter, and there's not a player in there that could possibly hurt him. I would even go so far as to say Tipsarevich in the 2nd round is his biggest stumbling block to make the semis, and that shouldn't be too difficult for him at all. He really drew a dream draw.
Nadal's 2nd round alone against Gulbis/Isner could prove interesting, but I personally think that if he survives the first week (which likely includes a game Youzhny in the 3rd round) he'll be your champion.
Djokovic drew a pretty easy semi path up until the quarters. Safin could be entertaining if they meet in the 2nd round. He should draw either Querrey, Del Potro, or Wawrinka in the 4th round, which shouldn't be a problem. Nalbandian, Baghdatis, or Karlovic could obviously pose a VERY stern test in the quarters.
Federer could have an entertaining match against either Nishikori or Monfils in the third round, neither of whom will back down from him. Gonzalez, Hewitt, or Ginepri await him in the 4th round, which is no cakewalk. He'll probably see Andreev or Berdych in the quarters, which would be less of a test than his 4th round (or maybe even 3rd round).
All and all, I think Roddick was practically gift wrapped a place in the semis. No matter what though, I can't wait to get this thing kicked off! GL to all your favourite players over the next two weeks...