It should be some sort of flash memory medium. Something physical, with enough space, portable and most importantly: hard to damage (stupid scratched cd's and dvd's). Flash drives or something like them should have replaced these a long time ago.
Comment on Re: The next successful successor to DVD as a medium for video will be:
Where are all the visionaries? It has to be a flash drive (hard to wreck) type medium. I think people will always want a hard copy. Chips rule, and make the most logistical sense.