Easily the best example for me.
Here's an overly long breakdown of why it's great and more than just a cameo:
It doesn't move the plot forward so much as it caps off a plot mini-arc while setting the stage for the final 1/5th of the film, and on a bigger level, it really demonstrates how lonely the Zombieland world is. A lot of important things actually happen at Murray's mansion that move the plot forward, even if Murray himself didn't have anything to do with it. But most importantly, it delivers one of the film's funniest scenes.
Tallahassee wanted to take a proper rest at an idol's mansion, and he got it. The group's time there really shows off how empty the country is, like Murray mentioning how he golfs by himself at one of the busiest courses and there's a shot of Tallahassee using $100s to dry his tears, showing that there's no hope of a return to a civilized, money-using society.
A lot of important things happen there. There's the flirting/relationship stuff between Columbus and Wichita. There's Tallahassee's revelation that he lost a son, and not a puppy as previously thought. Then, there's the girls' ditching of the guys, showing the dog-eat-dog point the world has gotten to, where even the 4 presumably now-solid friends was just a pipe dream and the girls taught the guys a lesson, again.
Then of course, there's the ACTUAL Bill Murray scene. The ghostbusters stuff was hilarious and I was surprised Murray was game for that. But the most obvious high point was him "pranking" Columbus and ending up getting killed. The theater was laughing for a solid 3-4 minutes after that. It's the epitome of the "it was just a prank, bro" meme gone wrong.
(btw, it's only a matter of time that this happens in real life, where some YouTube kid tries even a harmless prank -- like wearing zombie makeup or a mask in broad daylight -- and scares a grown ass-man with an open-carry license and gun and the kid is shot out of a fight or flight reflex (most people instinctively run when they see a "freak," but there are those who fight). We've already seen multiple instances of pranksters getting actually physically attacked just as a reflex of being frightened; imagine people with firearms who get frightened. It's going to happen 100% one of these days).
Anyway, that's why the 8-10 minutes were the best part of the film, and I am soooooooooo glad it didn't get spoiled for me.
TLDR -- Bill Murray is the man, and him falling victim to the "it was just a prank, bro!" sequence was pure comedic gold. "Is this how you say hello where you come from?" is EXACTLY what Bill Murray would say after getting shot. Best secret appearance of all-time, it's an indisputable fact.