If I had to pick one I'd say Shawn Michaels. I could see it coming but it was a shock to almost everyone and he was the HBK of old, with the Cowboy hat and the stubble.
I would also just like to mention that it is ridiculous that so many superstars, with the exception of Jericho, have needed to make returns due to injury in the last couple of years. Batista, Mark Henry, Rey Mysterio, Triple H, Shawn Michaels, Undertaker, Edge, The Boogeyman, Bobby Lashley, John Cena etc...
And how many times recently has a title had to be relinquished due to injury? I count at least 3.