Zeppelin vs Pterodactyls was an idea Hammer floated around but never went with around the early 1970’s. Given the budget these used around then it may have been an eyesore, but I would have loved to have seem them give it a try.
The Invisible Man-Despite having adapted a number of other classic monsters that Universal did it was never mentioned that Hammer considered doing the Invisible Man. A shame as I would have loved to have seen them give it a go around the mid-1960’s.
Another Captain Kronos film-When Captain Kronos Vampire Hunter was made Hammer had the idea of making a series of these with Kronos as a time traveling vampire hunter. I wish they had gone with that.
Another Sherlock Holmes film shortly after the Hound of the Baskervilles-Peter Cushing would get to play Holmes again only TV and a decade after the Hammer film. I likes Hammer’s take on this tale and wished they had done another Sherlock Holmes film right after this.
Another werewolf film-Hammer did four mummy films, even two Dr. Jekyll films but only one werewolf movie in The curse of the werewolf. Rumor is that early drafts of the 1972 film Demons of the mind had characters being werewolves but by the final draft they just had mental problems. I wished that Hammer had tried another werewolf film at some point.