Jossed: A scientist baring a striking resemblance to Strange appears in a flashback to Bane's origin story on how he received Venom. While helping to create a Genius Bruiser, giving him a Fantastic Drug to make him bulkier, and unleashing him against Batman is exactly the kind of thing Strange would do, it wasn't him, and seems to be a coincidence.
Name's the Same: The name "Red Robin" sure would sound more intimidating if it weren't the name of a fast food franchise. Especially if their slogan weren't:
Red Robin! Yuuuuuum!
Cassandra Cain to Kate Kane, at least in terms of sound.
And Katherine "Kate" Kane to Cassandra Cain, sound-wise.
A very confusing example with Doctor Simon Hurt. Lincon March also claims to be Thomas Wayne Jr., and may in fact be Bruce's long-lost brother.
Recycled Script: One of Hugo Strange's earliest stories had him unleashing a fear-inducing powder on Gotham City; the Scarecrow debuted less than a year later (though he didn't use his fear gas then).
What Could Have Been: This image◊ was created in case Jason Todd was voted to survive A Death in the Family. A very similar colored version (here◊) was printed in Batman Annual 25, which recounts Jason Todd's resurrection, as well as the reality-warping that caused it.
Dick was going to be Killed Off for Real in Infinite Crisis. For the same reason that saved him in fact. Considering how much emotional weight came from Barry Allen's death he could have been gone a while...
In the early 00's, there was brief talk at Warner Brothers of possibly making a live action Batman Beyond movie to reboot the Batman franchise but the idea was passed over for Batman Begins instead.
Hawkfire almost got featured, alongside Beast Boy and a host of other 1970s characters, in a spin-off called Titans L.A. As Bat-Girl, she was initially set to be part of the main '70s Teen Titans team and be involved in a love triangle with Robin and Duela Dent, but DC pulled the plug on the title before Bob Rozakis could get to those plans.
Awesome, Dear Boy: The reason several of the guest-stars took the gig as villains. Victor Buono as King Tut is the best example: he was a huge (no pun intended) fan of the comics, and was so into the series he made more appearances than any other guest-star outside of Newmar, Romero, Meredith, and Gorshin.
Beam Me Up, Scotty!: Sort of. Robin's infamous "Holy [relevant phrase]!" Catch Phrasewas used constantly, but he usually didn't end it with "Batman!". He did occasionally, but not nearly as much as the phrase's popularity would make one think he did.
Briefer Than They Think: The series only ran for a year and a half from 1966-68, but since most of the series' stories were two parters, that means 120 episodes were produced for a suitable syndication package.
Spencer Tracy was offered the role of The Penguin, but would accept only on the condition that the series got to end with him killing Batman.
Also, Two-Face was once considered as a villain for the show, only his origin would be that he was a TV news anchor who had a TV set blow up in his face. Clint Eastwood was even considered for the role but the character was ultimately dropped because he was considered "too gruesome" for such a light-hearted show.
The season 2 episode "The Puzzles Keep Coming/The Duo is Slumming" was originally written for the Riddler, but with Frank Gorshin having contract disputes with the producers, the similar Puzzler was created instead.
Tim Burton once said of the film "I liked parts of it, but the whole movie is mainly boring to me. It's OK, but it was more of a cultural phenomenon than a great movie." He also wasn't horribly enthusiastic about how Prince's songs were used in the film.
Main screenwriter Sam Hamm, one of the many writers who worked on the script, has also absolved himself from the sequence where Alfred leads Vicki to the Batcave, a move that didn't sit well with a lot of fans. Hamm said the scene didn't come from him and that the day Alfred let someone in the Batcave would be his last day of employment. It gets a Call Back in Returns.
The Danza: Jack Nicholson as (pre-Jokerization) Jack Napier.
Enforced Method Acting: Keaton hated the Batsuit because he suffered from claustrophobia. Elfman and Keaton both decided that it would enhance his performance. And it did.
Executive Meddling: This was a big reason the Schumacher films turned out the way they did, but again, Burton's films weren't immune.
The Axis Chemicals set was originally the xenomorph hive from Aliens. The crew had to remove most of the xenomorph webbing before filming, but bits of it can still be spotted if you look carefully enough.
In the original script, written by Tom Mankiewicz, crime boss Rupert Thorne hires Joe Chill to murder Thomas Wayne because he is running against Thorne for city council.
A later draft written by Sam Hamm also has a large part of the film concentrating on Bruce traveling abroad and training with Henri Ducard, whom Bruce would later discover to be a film. This script was later overhauled into the version seen in the film, and Ducard was deleted. Months before the film's release, then-DC Comics editor Denny O'Neil asked Hamm to guest-write a "Blind Justice" storyarc throughout Batman-themed comics as a tie-in, and Hamm introduced his character there (specifically, in Detective Comics #599, April 1989). Ducard would later appear, played by Liam Neeson, as a Composite Character with Ra's al Ghul in Batman Begins.
Burton stated in an interview that he had initially wanted Adam West and Julie Newmar, from the 1960s series, to play Thomas and Martha Wayne in the flashback. Audiences would recognize West and Newmar from the series and see them get shot, symbolizing the "death" of the old Batman. Script rewrites caused this to be scrapped, and West later said he wasn't even offered the role (and even if he was, he wouldn't have taken it).
Sean Young was originally going to play Vicki Vale before Kim Basinger. Young had to bow out at practically the last minute after breaking her collarbone in a horseback riding accident.
That hooker who smiles at Little Jimmy in the film's opening scene? Originally, she was supposed to be only 14 years old. She was also going to be shown chatting casually with a couple of cops, showing us how corrupt the Gotham police are even before we meet Eckhart.
Some of the earlier drafts focused on Batman's origins and featured Robin.
This film went through so many different directors, screenplays, tones (including but not limited to straight up Adam West style parodies) and possible casts before we got the film we know and love today that there are truly too many to list here. Legend has it that Richard Donner himself, the man who directed the 1978 Superman film, was among the directors approached at one point to make this film, but had to decline due to previous commitments. Actors considered for Batman included Mel Gibson, Pierce Brosnan, Charlie Sheen, Tom Selleck and even Bill Murray opposite Eddie Murphy as Robin.