These would be my picks.
Mash - Radar informs us Col. Blakes chopper went down
Dr.Who - Van Gohh at the museum
Futurama - Digging up his Nephews grave
Futurama - Jurrasic Bark
That Mash episode destroyed me as a child. It took decades for me to trust the TV again.
Then the Jurassic Bark incident happened, and I will never trust the TV with my emotional well being again.
Honorable mentions:
Scrubs - Dr.Cox looses his shit
Edit:
Just remebered this one Fresh Princes father ditches him
Those Futurama episodes get you right there. The Lars episode/movie as well as Fry's mom (episode Game of Tomes) also hit hard. I've underestimated how powerful that show can be. Damn near cried just watching that clip again.
The Boy Meets World final scene. It jumps around and the top seems a bit cut off but it's the best quality I could find.
Also from Boy Meets World, when Shawn and Jack's father, Chet, passes. Extra moving since Jack only first met Chet earlier that season.
And finally, from the same show Plays with Squirrels. This is something of an "alternative timeline" scene; everyone moves on, goes their separate ways, and don't maintain the bonds they've formed. The artist formerly known as Eric Matthews comes back and shares his manifesto, showing how things should have been.
I'm sure there are others, including others from other shows, but that's all I could think of right now.
EDIT:
Found another. Roseanne - Aunt Jackie beaten. John Goodman getting his jacket at the end has a lot of power in its own way, and I'm not talking about his bulk.