it can be as obvious/cliche or obscure as you like.

Lost - Whenever i think of Lost the first thing i often think of is the Submarine scene a few episodes before the last one. Maybe because it sticks in my memory as it was more recent and i haven't re-watched it yet, but when they came out of the submarine and onto the beach. It just hit me. Hard. Probably the only time i've bawled out watching television.

Twin Peaks - Probably cliche but the original dream sequence. In the context of the rest of the show up to then it was just a mind fuck. Talk about confusion, mystery, awe and mind fucking all at once.

The Wire - when Stringer got shot.