Video compression seems like a big one. So does FFT. Even if they were conceptually around for a long time (Gauss instead of Tukey probably originated FFT, Fano

Video compression seems like a big one. So does FFT. Even if they were conceptually around for a long time (Gauss instead of Tukey probably originated FFT, Fano -compression in general, etc), particular implementations of them made for huge differences in what people could do with computers. If not compression, certainly coding theory in general, which is so all-pervasive now, people forget it exists.