Teleportation technology from Star Trek, I could annihilate the transport industry and make masses of cash. And best of all, we can shut the hippies up about how we all need to go vegetarian and Formula 1 needs 4-cylinder engines. The car and aeroplane will be relinquished for recreational use.
Out of the things that actually exist and don't smack of megalomania: Knowledge, always knowledge. I'd like my MEng in Aero engineering, sure, but I'd like to be able to understand so much more. Astrophysics, for example, usually flies over my head.