The Internet, for sure.
The advances in PC technology and optical fibre communications were fairly predictable based on the trend extrapolations the Profs at Uni were putting out way back when but the ability of the internet to totally transform every aspect of society was not.
Jeez, when I think that just 25 years ago I was punching a stack of paper cards to program a whole floor full of hardware in Fortran 77 to work out some daft equations 'overnight' (assuming you didn't drop the whole lot and screw up the order of the control cards ), the mind boggles as to just how far we have come !