There are only probably a handful of sitcom finales that flash forward, so this is more of a discussion on how you feel about those kinds of endings more than it is a list. But just for lists sake, I’ll name all the ones I know of…

Mad About You (1999) - “The Final Frontier”
Will & Grace (2006) - “The Finale”
How I Met Your Mother (2014) - “Last Forever”
Parks & Recreation (2015) - “One Last Ride”

Does anyone know of any other sitcom finale that shows future years for the characters? The Office kind of did. It was set one year after the second to last episode. But I’m referring to shows that went way into the future and not just for one little scene but the main plot of the episode takes place using scenes of the future.

How do you feel about those kinds of endings?

I personally don’t like it. I don’t want to know the full on future for these characters. I like leaving them in the finale and I can imagine what happens to them afterwards, or wait for the reunion movie, lol. The only one it worked on was How I Met Your Mother and that’s because the whole show was a future Ted telling his kids how he met their mother. He just sped up the story in the final episode.

Frasier sort of did that in the episode Rooms With a View. Daphne was walking down the hallway after seeing Niles after his surgery. She paused in front of a doorway for a moment and then we saw Niles holding their little girl, and Daphne was holding their newborn baby girl.
Niles: "Meet you new sister."
Daphne: "Look, she's smiling at you."
Even though Niles and Daphne's first child was a boy, it still gave us a glimpse into their future.

The Fresh Prince of Bel-Air did it on the episode where Nicky was christened. It opened with Nicky as a little boy and Phil coming in to tuck him in. Nicky asked his father to tell him the story about his christening. We see the story throughout the rest of the episode and then it ends with Nicky asking to see his godfather and that's when we find out that Geoffrey is his godfather.

The King Of Queens: China Syndrome Part 2 goes one year into the future at the very end of the episode to show what their home life looks like having 2 kids.

the CHEERS finale showed Sam & Diane in the future.