To mix it up a little bit, when Ryan got the promotion in the Office at the end of season 3. That came completely out of nowhere.
In Breaking Bad, when Hank finds Walt's copy of "Leaves of Grass." That scene was crazy because you KNEW being the end of the mini-season that something big was going to happen, and the scene played so peacefully, with the family happily barbecuing on a Sunday afternoon. I was waiting for someone to come busting in to attack Walt for getting out of the game. So tense. And then Hank sits down to take a crap. Awesome stuff.