Actually, less than half of these are Christmas episodes or specials, but that's okay, because "It's a Wonderful Life" itself isn't technically a Christmas movie. Still, it's associated with Christmas to a sufficient degree that a fair number of episodes that "borrow" the plot are Christmas episodes. As for the ones that aren't... well, I wanted to include them here, anyway. (Of course, not all of the things listed here strictly follow the plot of the movie, but the important thing is getting a glimpse of a possible alternate reality, to see how many differences- usually bad ones- can be caused by just one difference, whether it's someone never having been born, or... whatever. There are lots of variations on the theme.) There are probably lots of "Wonderful Life" parody episodes I haven't included here, if I'm sure I haven't seen them and I'm not sure I'd be interested in seeing them; I'll try to list things that I think I'd probably like to see. But some of the things listed on my Christmas episodes pages but not here may involve these tropes, if I've forgotten that they do so.
Episodes on this page are listed in chronological order of original airdate.

Aired in 1979, in season one of Mork & Mindy. Not a holiday episode, but Mork gets to see what Mindy's life would be like if he'd never come to Earth. I doubt I ever saw this (or if I did, I was far too young to remember it), but I'd like to.

Aired in 1984, in season six of Benson. I don't think I ever saw this, but I'd like to.

Aired in 1986, in season three of Moonlighting. I have no idea whether I saw this or not, but I'd certainly like to.

Aired in 1986, in season twelve of Saturday Night Live. Apparently SNL has done at least a few actual parodies of "It's a Wonderful Life," but I don't think I've seen any of them. This sketch isn't actually a parody, but it's something I remember quite fondly. (Though I don't recall whether I actually saw it when it first aired, or as seems more likely, some years later in a retrospective of past Christmas episodes.)

Aired in 1987, in season nine of The Facts of Life. I have no idea if I ever saw this, but I did used to watch the show.

Aired in 1988, in season two of Beauty and the Beast. I don't think this is a holiday episode, but I don't recall whether or not I even saw it. I'd certainly like to.

Aired in 1989, in season three of Teenage Mutant Ninja Turtles. Not a holiday episode, but the turtles get to see what the world would be like if they'd never been mutated. I have no idea if I saw this episode or not, but I'd certainly like to.

Aired in 1991, in season eight of Night Court. Not a holiday episode, but Mel Tormé appears as Harry's guardian angel to show him what his coworkers' lives would be like without him.

Aired in 1991, in season fourteen of Dallas. Not a holiday episode; actually, it's the series finale. An "angel" named Adam shows J.R. what life would have been like for his family without him. I don't remember any particular details except the very end of the episode, but this is one of the shows that I best remember the fact of having done this kind of episode.

Aired in 1991, in season four of Beetlejuice. Not a holiday episode, but Beetlejuice gets to see what his friends' lives would be like without him. I'm pretty sure I never saw this, but I'd like to.

Aired in 1991, in season four of Garfield and Friends. Not a holiday episode, but Wade's guardian angel shows him what life would be like for his friends without him. It's a pretty silly story (which is typical for the show), but it's probably the thing that most often comes to mind when I think of "It's a Wonderful Life" parodies.

Aired in 1992, in season three of "Tiny Toon Adventures." I've actually never seen it, since I didn't really watch the series, but it's something I'd like to see someday.

Aired in 1993, in season three of The Fresh Prince of Bel-Air. Not a holiday episode, but in one scene, Tom Jones appears as Carlton's guardian angel to show him what his family's life would be like without him.

From 1993, this is a short film that was produced for BBC Scotland. It's a dark comedy about Kafka trying to write "The Metamorphosis," and the "Wonderful Life" parody is barely there, but... it's interesting. And very weird. Definitely worth a watch.

Aired in 1996, in season two of The Secret World of Alex Mack. Not a holiday episode, but when Alex wishes on a star that she'd never been born, she gets to see what her family and friends' lives would be like without her.

Aired in 1997, in season four of Space Ghost Coast to Coast. It's not a holiday episode, and the "Wonderful Life" parody only happens in a brief scene after the end credits, when Zorak wishes he'd never been born, and his dead nephew, Raymond (who is now an angel), shows up to tell him what the world would be like without him.

Aired in 1998, in season three of Buffy the Vampire Slayer. Not a holiday episode, but when Anyanka grants Cordelia's wish that Buffy had never come to Sunnydale, we get to see a much darker version of the world.

Aired in 2000, in season one of The Zack Files. Not a holiday episode, but Zack gets to see what the world would be like if Vernon were class president.

Aired in 2001, in season four of That '70s Show. Not a holiday episode, but after Eric and Donna break up, an angel shows Eric what his and his friends' lives would be like if he and Donna had never been together. I don't remember whether I ever saw this episode or not.

Aired in 2003, in season two of The Dead Zone. Not a holiday episode, but Johnny's psychic ability gives Bruce a vision of what life would have been like for both himself and Johnny if they'd never met.

One segment from a 2005 episode, in season two of Hi Hi Puffy AmiYumi. Not a holiday episode, but Yumi dreams that she never joined the group, and gets to see how that changed Ami and Kaz's lives.

Aired in 2006, in season one of The Emperor's New School. Not a holiday episode, but after making a wish not to be emperor, Kuzco sees what life would be like with Yzma as empress.

Aired in 2006, in season one of Kappa Mikey. It mashes together "A Christmas Carol" and "It's a Wonderful Life," among other things.

Aired in 2008, in season seven of Smallville. Not a holiday episode, but Jor-El shows Clark what the world would be like if he'd never come to Earth.

Aired in 2008, in series four of Doctor Who. Not a holiday episode, but it has the plot (sort of), with Donna seeing what the world would be like if she'd never met the Doctor. (And despite not being a Christmas episode, it does include callbacks to the second and third Christmas specials.)

Aired in 2008, in season two of iCarly. When Carly wishes Spencer were more normal, her guardian angel grants that wish, and she gets to see what life would be like if her brother weren't such a goofball.

Aired in 2010, in season five of Psych. Shawn has a dream in which Tony Cox (dressed as an elf) shows him what life would have been like for his friends and family if he'd never returned to Santa Barbara and become a detective.

Aired in 2011, between seasons three and four of Warehouse 13 (though set within season three, I guess). An artifact sends Pete into a reality where he was never born.

Aired in 2012, in season four of Glee. One segment of the episode features a dream sequence in which Artie sees what life might have been like if he'd never been paralyzed.

Aired in 2014, in season seven of Castle. Not a holiday episode, but an Inca artifact sends Castle to an alternate reality in which he and Beckett had never met.

Aired in 2017, in season one of The Mayor. When Courtney realizes the city's budget won't allow him to deliver on his promise to provide people at a homeless shelter with a great Christmas, he thinks Fort Grey would have been better off if he'd lost the election. So in a dream, an angel (in the form of his mother) shows him what the city would be like with Ed Gunt as mayor. After having his epiphany and waking up with a renewed spirit, he decides to do his best to help the homeless shelter, even if he can't give them a perfect Christmas. And he unwittingly inspires many of the town's citizens to help, as well.

Aired in 2018, in season 44 of Saturday Night Live. Donald Trump (Alec Baldwin) wishes he'd never been elected President, and an angel (Kenan Thompson) shows him what the world would have been like if Hillary Clinton had won. (I really wish I could live in that world.)