Let Us Consider the Macguffin

The Macguffin is a story trope, the concrete goal that everybody in the story is chasing. Obviously not every story has a MacGuffin, but a great concrete goal can make a story much easier to write and understand. Charlie Jane Anders has a post on io9 asking about the greatest Macguffin in SF and fantasy, and the answers in the comments are a lot of fun; Tv Tropes has a slightly more precise definition that’s also a lot of fun.

Standard warning for TV Tropes: if you go in there and start to click on the links, you won’t come out for hours. Of course, I clicked. And now I want to write a story about an Egg Macguffin, which is a Macguffin that’s an egg.

Okay, that’s not really an egg, but it’s egg-SHAPED.

I like working with Macguffins, but I don’t use them much. They require a particular kind of chase/action story that I don’t write very often. Faking It had six paintings as a MacGuffin; the protagonist had to get all six to keep her secret identity a secret. In the novella, “The Hot Toy,” the Macguffin was a military doll called Major MacGuffin. Yes, I have no shame. Other than those two, I don’t think I’ve written a MacGuffin, so I must remedy that because I really like the little suckers. My fave may be the suitcase from What’s Up, Doc?,” but I know there are other great ones.

So here’s a question: What do you think of MacGuffins as a plot trope, and if you like them, what are some great ones (books, movies, TV, comics, we don’t care as long as it’s story)?