A seasoned game master, S. John Ross has compiled a "big list of RPG plots" which is spectacularly thorough and funny. He's boiled down nearly every RPG scenario I've ever experienced into one of 34 possible situations, from the obvious "Capture the Flag" (duh) to the odd "Long or Short Fork When Dining on Elf?" (players must open up diplomatic relations with a strange culture). He characterizes the overused "Quest for the Sparkly Hoozits" plot thusly:
He also comes up with some interesting twists on the "Help is on the Way" plot, where players must rescue people/a nation/a galaxy:
I noticed that he doesn't include my very favorite RPG plot, "Naked and on Fire in a Strange World." But maybe it could be subsumed under "Not in Kansas," in which the players "are minding their own business and find themselvestransported to a strange place."
The Big List of RPG Plots [website]