Recursive Adaptation: The late 90s/early 2000s Sabrina animated series (and its versions of the cast, etc.) was adapted back into the comics, in the context of being flashback stories to Sabrina's junior high years.
When Tim, played by George Wendt of Cheers fame, walks into Hilda's coffee shop in a later episode, everyone raises their mugs and greets him, "Tim!".
Aunt Irma is played by Barbara Eden, who also played in another supernatural sitcom. Her magical gesture in both? Crossing her arms.
Robin Ricker plays Cousin Marigold, the mother of a bratty witch daughter. Around the same time she also starred in the Buffy the Vampire Slayer episode "Witch", where she also played the mother of a witch daughter or so we think as the episode goes on. Buffy even says during the episode "she's our Sabrina".
David Lascher previously played a character called Josh in Clueless - which had a crossover with this, featuring Sabrina.
This is not the first time Phil Fondacaro has played a troll.
Britney Spears guest stars in the Season 4 premiere to perform "(You Drive Me) Crazy". Melissa Joan Hart had a movie coming out at the time that was titled Drive Me Crazy after the song - and she and Adrian Grenier appeared in the video as a tie-in. Clips of the video are shown in The Stinger for the episode too.
Penn Jillette plays Drell, head of the Witches' Council. In real life he performs as part of a magic duo Penn & Teller.
Casting Gag: In one episode, it is revealed that Aunt Hilda (played by Quebec-born Caroline Rhea) failed to fill out her immigration paperwork, and when tested on the legality of her citizenship by reading a sentence, she reads it in an exaggerated Canadian accent. She is then promptly deported to "the Northern Sector of the Other Realm, where she came from." Subsequently, she is traded for badger pelts.
Channel Hop: Moved from ABC to The WB. As a result, most of the cast members aside from the Spellmans, Salem and Josh were fired (though Harvey was brought back eventually after fan protests).
Contractual Purity: Melissa Joan Hart had grown up by the time Clarissa Explains It All had ended but her mother didn't want her to pursue adult roles. This however was less about purity and more because she saw the business potential of marketing towards Melissa's strong kid/teen fanbase. Melissa did however send Archie Comics into a frenzy when she appeared in Maxim around the time the show was airing. Archie are infamously protective of their 'wholesome' brand, never mind that Melissa was twenty-three when the issue came out. According to Word of God, the main backlash was from the magazine advertising Sabrina posing rather than Melissa - making it look like she was doing it in character.
Creator Backlash: Caroline Rhea pokes fun at the terrible wardrobe choices on the show, saying Sabrina went to school "dressed like an accountant" and that Hilda looked like she was "going to a coronation for a very senior royal member."
Dawson Casting: Pretty much the whole "teenage" cast but notably Melissa Joan Hart (Sabrina) (b. 1976), Jenna Leigh Green (Libby), (b. 1974) and Lindsay Sloane (Valerie) (b. 1977). One of the student extras was a balding man!
According to Michelle Beaudoin, the reason Jenny was axed was because the network wanted Sabrina to have an 'ethnic' best friend. This is odd, seeing as her replacement Valerie wasn't ethnic (unless being half Jewish counts). Sabrina does gain an ethnic best friend in Valerie's replacement Dreama.
Harvey was dropped in Season 5 because producers felt Sabrina "needed to leave that high school baggage behind". Due to negative fan reactions, he was brought back in Season 6.
Miles got dropped from the last season due to budget cuts and because producers felt fans weren't responding well to his character.
Fake American: Canadians Ryan Reynolds, Michelle Beaudoin, Lalainia Lindbjerg and Laura Harris in the Pilot Movie. Although technically the movie is set in Riverdale (as opposed to the show's Westbridge) and Archie Comics have said that Riverdale could be anywhere - including Canada. Which would make Melissa Joan Hart a Fake Canadian in that case.
Similarly to M*A*S*H, very few actors carried over from the original Pilot Movie to the series proper. Other than Melissa Joan Hart, only Michelle Beaudoin, who played Marni in the movie and Sabrina's (first) best friend, Jenny, in the series, appeared in both of them. Hilda, Zelda, Harvey, and the voice of Salem were all re-cast. Libby does not appear in the pilot; a character named Katie fills a similar role. There's also a character named Seth in the movie who acts as Wrong Guy First; he has no analogue in the series, as Sabrina is hot for Harvey (which is more or less requited) from the outset.
A more conventional example, during the show's run; Sabrina's father was first played by Robbie Benson in Season 1 and Doug Sheehan in Season 4 and 7. Notable because the latter looked several years older.
Cousin Marigold is another example, first played by Robin Ricker and later Hallie Todd.
Real-Life Relative: Recurring character Amanda (Sabrina's evil cousin) was played by Melissa's little sister, Emily Hart. Who, as noted above, ended up playing Sabrina herself in the cartoon. Likewise Amanda's little sister Allie is played by another Hart sibling - Alexandra Hart-Gilliams.
Reality Subtext: The Season 4 premiere has Britney Spears being zapped into Sabrina's room to hang out briefly. According to Melissa Joan Hart's autobiography, this parallels how when they were filming, Britney would not be allowed to go to lunch with the other cast mates - because her entourage insisted on her doing more work.
Sleeper Hit: ABC didn't really support the show in its early days, favouring Clueless instead. Sabrina ended up as the highest rated show on the network for four years.
So My Kids Can Watch: Martin Mull played Mr Kraft in order to impress his daughter, who was a fan of the show.
Throw It In!: The Seasons 5-7 opening sequence has a moment where Melissa Joan Hart leans back on the bed but smacks her head off the wood, and she can be seen rubbing her head.
Sean Laughton appeared in various episodes throughout the first three seasons as cops and firemen, but also starred as Valerie's boyfriend Ken in Season 2's "The Equalizer".
Charles Shaughnessy played Hilda's egotistical date Alec in 'You Can't Twin' and reappeared later that same season as James Hexton in 'Witchright Hall'. (This second appearance is probably because Shaughnessy was planning to star as Hexton in the series that 'Witchright Hall' would have become had it been picked up by the network.)
Donald Faison had a small role in Season 1's "Magic Joel" as a student called Justin. He reappears in Season 2 and 3 as Dashel - another half-mortal witch who is Sabrina's love interest.
A variation. The puppet used for the cat Juliet in season 4 is the same one used for Hilary in Sabrina Down Under. What makes this hilarious is that they're both cursed witches and Salem falls for both. Perhaps the Witches' Council are just lazy when turning witches into cats.
They attempted two spin-offs with Amanda. The first would have been about her, Allie and Marigold moving in with Emile and his boys - one of whom played by Frankie Muniz. The second would have focused on her hijinx at Witchright Hall. Neither happened, though Emily Hart did get to voice Sabrina in the Animated Adaptation.
The plot of Season 7 would have revolved around Josh proposing to Sabrina and the growing love triangle with Harvey. When David Lascher opted to leave the show, Aaron Jacobs was created to fill his role. Additionally they wanted a two-part finale but were only granted one episode.
Some plans for a Season 8 would have involved Sabrina and Harvey moving into a haunted house. Barbara Eden would have joined the show as a regular.