Twilight Zone Episodes that were ...

There are a surprising number of these, if I'm remembering correctly.

"Twenty Two" (S2:E17) was based on "The Bus-Conductor," which was previously filmed in Dead of Night (1944), though I think the TZ version is eerier and better.

Several of the other "evil dummy" episodes ("The Dummy," "Caesar and Me") are based on another great segment in that movie, the "Ventriloquist's Dummy" sequence.

"Queen of the Nile" (5:23) borrows a great deal from Sunset Boulevard.

"King Nine Will Not Return" (2:1) was based on the real-life disappearance of the Lady Be Good in 1943, an incident which was previously fictionalized in February 1960 (just a few months before the TZ episode) as "Ghost Bomber" on Armstrong Circle Theatre. It would later be fictionalized as the telefilm Sole Survivor in 1970 (Sole Survivor being, of course, the answer to the famous "what is my movie?" question on the old boards).

Thank you so much for your far-too-kind words, Mszanadu!

As I noted on the other thread, I wonder if "Number 12..." were partly based on Huxley's Brave New World--but of course that hadn't been filmed at that point. (It still hasn't received a feature-film, big-budget adaptation as far as I know.) I believe that Scott Westerfield's Uglies series (of which I've read the first book) borrows (a euphemism for "steals" ) its entire premise from this episode (Mr. Westerfield's protestations to the contrary notwithstanding). 

It seems to me that "Black Leather Jackets" (5:18) was based on Brando's The Wild One (with aliens added, of course). 

Also, not exactly what you're looking for, but a few connections between episodes: "Walking Distance" (1:5), "A Stop at Willoughby" (1:30), and "Of Late I Think of Cliffordville" (4:14) all have the same general theme--a man wishes to return to his hometown and experience his boyhood. Of all these, ironically, the first, "Walking Distance," seems to be the most mature, recognizing both the good and bad of nostalgia. 

Also connected: "Where is Everybody?" (1:1), "Third from the Sun" (1:14), and "I Shot an Arrow into the Air" (1:15) (and Serling's script for Planet of the Apes)--same general set-up, same general twist ending--and "King Nine Will Not Return," "The Arrival" (3:2), and "The Odyssey of Flight 33"--same general aviation theme, probably suggested by Rod's pilot brother Robert.

P.S. In researching that last tidbit, I found an interesting piece of information I never knew. On an airplane-centered forum (I didn't know those existed either!), posters were discussing The Twilight Zone, and someone wrote, "'The Arrival' was rather good at first too. It's not every day that you see a DC-3 land with nobody on board. I guess something similar really did happen with a DC-3, in 1957 in Missouri. Only in that case it was a cornfield rather than at an airport, and there was no eerie mystery." Does anyone know anything about this real-life incident? I'd never heard of it. 

P.P.S. Robert J. Serling, Rod's brother, penned a number of aviation-related books, one of which was The President's Plane is Missing--later turned into that well-known telefilm of the same name. How's that for connections?