Reader's poll: What's the world's greatest invention?

So, we learned during the opening ceremony for the Olympics, the four great Chinese inventions are paper, gunpowder, movable type, and the compass.
So what's so great about that stuff?
You want a great invention, the greatest ever -- in my opinion, anyway? It's the automatic dishwasher.
Wheels and pulleys are great, don't get me wrong. But the most significant thing about their invention is that they laid the way for the ultimate invention of the dishwasher. And yeah, I know movable type is great stuff (whether credited to Gutenberg or the Chinese), but the greatest thing about it is that it made it possible to create owner's manuals for automatic dishwasher.
For a moment, I was ready to nominate spray-on sunscreen for the GIE (greatest invention ever). And it is great stuff, but next year something better will come along.The dishwasher is timeless.
Stovetop popcorn makers are pretty good, but they're no dishwashers.
If you've got something that you think would top the dishwasher in the inventions ratings, I'd like to hear about it.