I always assumed it was called a money shot because the girl got higher pay for the scene (I think she deserves it). But, in another thread somewhere, someone suggested that it was the guy who got the bucks, or simply that flicks with that scene brought in more money.
Anybody know for sure how this term originated?
No cite, but I’d always heard it as the last option – these shots were the ones that would make the film popular and profitable.
I’d go with that second one, too. In the world of the adult film, it’s not as though there’s this one huge scene that costs more than any other scenes and therefore gets that appellation.
In the real filmmaking world, the opposite holds true. I’ve heard the term a few times on set, and it does indeed refer to the shot or set-up that costs the production the most money. In that arena, it really means, " show me the money". Biggest EFX, biggest explosion, longest car chase, most extras, however you spend your money.
As the Director of Photography of True Lies ( who I believe was Russel Carpenter,A.S.C. ) said in an interview once,
For him I guess THAT was the money shot, or money shots.
Or, maybe in the crude world of porn, ejaculations are viewed as priceless? 
Cartooniverse
Here’s JE Lighter: 1981, NYT article,“Since special ability parts, silent bits, and, occasionally, stunts–all of which are known as “money shots”–are usually given out spontaneously on the set as the scene calls for them, a smart extra will stay alert for opportunities.” “I can clear $300 to $400 in a three-day week with overtime, if I can get in a money shot,” says Gina Picerni. “If the timing seems right, I’ll go up the A.D.(the assistant director) and ask if there will be any money shots.”
Lighter’s info on the sexual connotation:
1989 article, L.A.Times; “These sexual numbers usually lead up to what is known as the “money shot”–a close-up of the male orgasm, sometimes filmed in slow motion. In her book, Willams quotes a 1977 porno film maker’s guide as recommending the use of at least 10 of these shots in a hard-core movie.”
In sports, the term “money player” meaning a guy who can deliver the goods, goes back to at least the 1920’s.
My opinion of the “money shot” is that it’s the “payoff”. That is, it’s what the audience is paying to see. The porn film connotation is obvious. In mainstream films it might be a “trademark” stunt, such as when James Bond skis off of a cliff in The Spy who Loved Me, and may or may not be at the climax of the film. Everyone cheered at Union Jack shot. Or it could be when the Hero finally “sticks it to” the bad guy. I think the “money shot” is the shot where the audience says, “Yes!!!”