Star Trek Transporter
We've all been there. You wake up and realise you're an hour late for work, so what do you do? If the Star Trek transporter existed, you'd simply press a button and hey presto -- you're at the office without even breaking a sweat.
Where the hell is it?
Breaking a human being's molecules down and teleporting them through space or assembling them from scratch at the other end is unlikely to ever happen. While there are many hypothetical theories, including 'fax' style copying of molecules and wormholes, the only thing that scientists have been able to 'transport' so far is light and single atoms.
I want one now!
The only reason that the Enterprise had a transporter room was because it was cheaper to use than filming the ship landing. So the closest you'll ever get to one, unfortunately, is an easyJet flight.