Henry Blake for sure. Gary Burghoff really nailed that last scene.
When Jack Soo (Yemana) from Barney Miller passed away, they did an episode in the squad room and each actor just talked to the camera about Soo and how much they loved him, and their favorite stories about working with him. In story, the character died, but that one episode where each actor just spoke from the heart was great. I only saw it one time, and I suspect that's one that didn't hit the syndication market.
I'm pretty sure I saw that one in syndication at least once.
Other than that, it's pretty much just Phillip J. Fry's dog.
Awww man, you just HAD to bring up Fry's dog.
Now it's getting dusty in here...
That episode "ruined" Futurama for me for years. Every time I tried to watch the series, all I could think of was that dying dog