Beam Me Up, Scotty!: The popular "Submitted for your approval" occurs in the opening monologue just three times. In contrast "In just a moment" occurs in the opening monologue 25 times, which makes this the most said four-word phrase that doesn't include "Twilight Zone". "In a moment" also occurs quite often.
The Danza: Burt Mustin as Burt the Bum in "Night of the Meek".
Edited for Syndication: The Christmas Episode "The Night of the Meek" features a holiday greeting from Serling at the end of his wrap up narration that was generally edited out. Also the fourth season hour long episodes were generally ignored until the Scifi Channel started running the show. Between the sixties and the nighties they were mainly shown only as edited together two-hour "movie" specials.
Hey, It's That Guy!: Almost too many examples to count. (Some are listed on the main page in the show description.) Many of them appeared more than once on the show.
June Foray played the Talking Tina doll in "Living Doll", essentially reprising the voice she did for the real life Chatty Cathy. She also dubbed over a child actor's voice in "The Bewitchin' Pool" using her Rocky voice.
If Kaa wasn't creepy enough, the creepy TV repairman in "What's in the Box" also has Winnie's voice.
On a related, but somewhat more pleasant note, John Fiedler (the voice of Piglet) appears as the mall owner in "Night of the Meek", as well as a subordinate angel in "Cavender is Coming".
Bob Crane, at the time an L.A. disc jockey, provided the voice of one on the radio in "Static".
The Mad Hatter was in "One For the Angels" and "Ninety Years Without Slumbering".
Malefecent can be heard briefly in "The Hitchhiker".
Lex Luthor was in "Cavender is Coming" and Sinestro was in "People Are Alike All Over" and "Ring-A-Ding Girl".
Quite a few people from Batman were in the series prior to the show:
The Penguin starred in "Time Enough At Last" as the meek Henry Bemis, "Mr. Dingle the Strong" as the titular meek character, "The Obsolete Man" as Romney Wordsworth, a librarian slated for execution for being well just read the title and "Printers Devil" as the devil himself, giving him the most starring roles on the show.
Alfred was in "Passage of The Lady Anne".
Police Cheif O'Hara was in "Nick of Time" as a mechanic, "The Grave" and "Ceasar and Me" as a pawnbroker.
The Mad Hatter was in "Escape Clause" as the devil.
Catwoman was a very sexy she-devil, in fact being the only female portrayal of the devil in this series in "Of Late I Think of Cliffordville".
The Bookworm was in "People Are Alike All Over".
The Archer was Santa Claus in "The Night of the Meek".
Shame was in "A Hundred Yards Over the Rim" and "The Dummy".
Dr. Cassandra Spellcraft was in "The Sixteen-Millimeter Shrine" as an aging film star longing to recapture her glory.
"Steel" was adapted into a feature film. Though it's somewhat subverted, as Real Steel, despite being based on the same story as "Steel," bears almost no resemblance to the story (outside of robot boxers). Additionally, the film is decisively more optimistic than the original story's dystopian setting.
What Could Have Been: In the original script for "A Game Of Pool," Jesse Cardiff loses to Fats Brown, but he doesn't die and he immediately begins practicing for a rematch
Orson Welles was originally planed to be the narrator but was too expensive.
Write What You Know: Many episodes took place in Upstate New York, where Rod Serling was from. Similarly, Serling was a vet of WWII (as were many of the other writers), which led to many a episode.