What's a useful replacement idiom for "money shot?"

You can use setpiece for the non-pornographic sense of money shot. It refers literally to movie scenes or sequences which require “serious logistical planning and considerable expenditure of money,” although it's also used more broadly to describe significant or climactic events in a story.

Notable examples of setpieces include the Snake Pit in Raiders of the Lost Ark, the Death Star Trench Run from the original Star Wars movie, the storming of the volcano lair in the James Bond film You Only Live Twice, and the burning oil rig in There Will Be Blood. Alfred Hitchcock referred to setpieces as crescendoes or "bumps" and tried to put three of them in each of his movies.

Edit: While setpiece works well for movies and elaborate stories, it may not be a good fit for short works and anecdotes. For those, you can often use punch line or zinger to refer to the linchpin of the joke or story.

Besides Bradd's good suggestions, there's also "focal point", "highlight" or my favorite "Pièce de résistance", defined below.

From Wikipedia:

Pièce de résistance (French pronunciation: ​[pjɛs də ʁezistɑ̃s]) is a French term (circa 1839), also called "plat de résistance" in France, translated into English literally as "piece of (or for) resistance," referring to the best part or feature of something (as in a meal), a showpiece, or highlight. It can be thought of as the portion of a creation which defies (i.e. "resists") orthodox or common conventions and practices, thereby making the whole of the creation unique and special. The phrase gives the sense that the referred-to element is the most outstanding, notable, or defining of the collection. For example:

Even with a diverse movie and television portfolio, Burnett's pièce de résistance will likely forever be The Carol Burnett Show.

Originally, the pièce de résistance was the most substantial dish in a meal, but now the term generally refers to quality, not quantity.