What's the greatest episode of television you've ever watched?

I would have to go with Buffy the Vampire Slayer The Gift Season 5 Episode 22.

Spoiler Alert:

It's the episode where she sacrifices herself to save the world, well again but it was where a lot of fans think the show should have ended because it was a nice ending to the series.

I personally liked that it went on because we wouldn't have gotten Once More With Feeling in season 6. One of the best episodes besides the Gift.
What's the greatest episode of television you've ever watched?
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