Flying car, etc.
As an emblem of the future, I think the internet--or the smart phone, if you want something tangible--is a far better than the flying car. It solves more problems, frees us more from restrictions, and more fundamentally changes what it means to be human. Flying cars are neat and Jetsonsey and all, but they have serious practical drawbacks balancing their advantages.
But I still love them. Because (much like smart phones) they help erode one of the classic arguments for intrusive government: the natural monopoly.
"Of course you need government regulating private economic relationships. Look at roads! What are you gonna do, have five competing private roads for every route?"
"Who needs roads?"
Okay, libertarian scientist-activists! Now let's get to work on a practical system of energy distribution that doesn't rely on physical networks! A fundamental improvement on small-scale solar, a superefficient and compact transportable storage medium, or some kind of remote transmission will do. Bonus points if it can be used as a death ray.