1. Marvel Cinematic Universe - The Multiple Appearances of S.H.I.E.L.D
The Films: The top spot goes to the Marvel Cinematic Universe because of how well setup the entire cliffhanger is. From the moment The Avengers was announced we knew it would involve SHIELD in one way or another, but subtleties in Iron Man, The Incredible Hulk, Iron Man 2, Thor and Captain America: The First Avenger all hinted as to what extent and how.
The Plots: There are too many to list here, so I will narrow it to SHIELDs involvement. Agent Phil Coulson begins the long running build up with his first appearance in Iron Man, with him and other SHIELD agents playing a large role in taking down Tony Stark/Iron Mans first nemesis, Obadiah Stane.
The Cliffhangers: Obviously Coulsons sudden major interest in Starks life serves to add interest to SHIELD. Next comes Nick Furys post-credit shocker as he discusses SHIELD with Stark, followed by Stark himself mentioning a team being formed in The Incredible Hulk in his own little cliffhanger. SHIELD pops up in the other films near the end too, just to really push the mystery further and further. Each tantalising detail and each film, edging closer to the finale of Marvels phase one, just served to up the ante for its arrival.
The Result: It goes without saying, really. The Avengers brought all the aforementioned heroes together flawlessly in an epic two hours, but it focused much more heavily on SHIELD than previous instalments. We finally see Nick Fury, Coulson and the other major players of the secretive organisation in action, as well as the famed heli-carrier. It was a perfect payoff to all the waiting, rumours, anticipation, hype, and of course the cliffhangers of the mysterious team that would go on to be The Avengers.